Overclocking
Simple Version:: Don't do it. Just don't. Don't Do it in any form!
Complex Version:: Other than the obvious degradation of the computer's life due to increased thermal output, you greatly increase the probability of data errors creeping in and compromising the reliability of your data.
MSDN Article on this
Intel vs AMD
Simple Version: Right now, Intel has the performance crown, while AMD has the value crown.
Power Supplies
Simple Version: Get a power supply from a known big name manufacturer like Asus, Corsair, etc.
Avoid no name "clone" manufacturers like the plague.
Add in a little bit extra power than what you need -- e.g. if your computer needs 400W, put in a 500W power supply.
Your computer does not need a 800 to 1,000 W PSU. Period.
Complex Version: The power supply is the one component in your computer, if it fails, can take down just about everything, from the motherboard to your hard drives.
So don't skimp on it.
The reason for adding a little extra power capacity (100W~) over what you need are:
1.) To provide a buffer for possible future upgrades -- you might want to add more internal hard drives in the future, or upgrade to a video card that draws more power than your older one.
2.) To provide an extra margin of durability -- PSUs designed for 500W when they pull only 400W, run cooler, and because they're built for a hotter thermal environment, last longer. This ties into the "if this fails it can kill everything else." bit about PSUs.
Motherboards
Simple Version: Buy from quality brands like:
Asus
Gigabyte
MSI
Intel
Supermicro (Good for workstations/servers)
Tyan (Good for workstations/servers)
Avoid deals that are "too good to be true".
Additionally, check the specifications of the motherboard carefully.
A specific model of motherboard with two SATA connectors may be fine for a simple media center (with a single optical drive and hard drive); but would not be acceptable for someone who uses more than one hard drive for storage.
How much memory can the motherboard handle? You want to be a little ahead of the curve in regards to total memory capacity, so you don't have to replace your board that often.
Complex Version: If the power supply is the heart of the computer, the motherboard is the brain. If you buy from a quality manufacturer (see previous list), you should have no problems, provided you do not overclock.
The reason for paying close attention to the boards' specifications in your initial buy is while there are Expansion Cards which can add extra SATA connectors/controllers to the computer; they generally are not as reliable as a built in motherboard connector/controller.
Memory
Simple Version: Buy from known major manufacturers like Kingston, Corsair, or Crucial. Buy memory within the same spec as the original memory; e.g. PC3200, if you are adding more memory to an existing installation.
Performance RAM isn't worth it, period.
Complex Version: Not much to add here really. Oh, and don't overclock.
Graphics Cards
Simple Version: Pick a card with a chipset from ATI or NVIDIA; and from a known manufacturer like BFG, etc.
Complex Version: Picking a card from a major chipset designer and then from a major manufacturer ensues that driver support and overall quality will be decent.
This is especially important if the hardware is an integrated graphics system -- avoid no name manufacturers or chipsets like the plague. Intel, ATI and NVIDIA are the ones to get in the integrated market.
Cases: Get a case from a major manufacturer like Antec. They tend to be put together a lot more sturdily than the cheap clone cases; and are much, much easier to assemble; tend to come with special thumb screws which sure beat using a screwdriver!
Example of Thumb Screw
Computer Assembly
If you're doing major computer assembly work; e.g putting together an entire system from the boxes they came in; wear an ESD Wrist Strap.
While computer parts are surprisingly durable (for example, I've had cards which have sat unprotected against other cards for nearly a decade boot up and run with no problems; but those are exceptions to the rule); you want to be sure that you haven't blown your investment in computer parts by shorting out a key component.
While you can RMA those components; it's annoying to wait for a new part to come in.
Minor assembly work; e.g. adding a new hard drive, or changing the memory in an existing system can be done safely by regularly touching unpainted metal parts of the case to ground yourself and dissipate any possible charge.
Do assembly in a relatively clean room or area. Do not do it in carpeted areas; and if you have any pets in the house, lock them out of the assembly area until the computer is assembled and sealed up.
Example: Cat comes up and rubs against you, while meowing; transferring a static charge from her fur to you.
Software
Picking the right OS
Traditionally, the rule of thumb has been to wait six months or at least one service pack release before buying a Microsoft OS. This was born in the very bad old days of Windows 95; and then reinforced by the bad release of Vista into an environment where a lot of hardware drivers weren't ready for it.
Nowdays, Windows 7 is actually quite nice, stable, and very compatible.
So the problem becomes one of picking the right version.
Essentially, Windows 7 Home Premium is all you really need if you're the average and slightly above average user.
If you handle some rather obscure software which needs virtualization via Virtual PC; Windows 7 Professional works quite nicely. As a bonus, it can handle 192 GB of memory; which is quite a bit more than Home Premium's 16 GB; but I think by the time we need more than 16 GB, we'll be near Windows 8's release.
Ultimate is just a waste of your money.
Advantages of going from x86 to x64 binaries
Simple Version:: If your programs need more than 2GB per process or 4GB total, 64-bit is good for you --phong
Complex Version:: Generally, the advantages from going from 32-bit to 64-bit are very small for most applications (5-10% performance improvement); and in many cases, there is actually a decrease in performance.
A good rule of thumb would be to look at the kind of datasets that are handled by the application/game.
An emulator for the NES for example, would not benefit much (if any) from an upgrade to 64-bitness due to the fact that there's only 2 to 32 kb of memory in the system being emulated.
By contrast, a graphics editing application that routinely handles very large images -- a 5000 x 5000 pixel bitmap at 24 bit consumes about 72 megabytes of information would benefit from 64-bitness, due to the fact that many graphics applications save "undo" steps so you can go back to a previous version of the image, and if you have several large images open at once, this causes huge memory requirements.
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This will do as a start; some other topics I have in mind are "you only need one antivirus program"; "personal firewalls are unneccessary, windows firewall works", and how to prevent browser hyjacks via the "map the whole thing as a bitmap so that no matter what button you push, the spyware installs."; and why to watch Windows Update; because sometimes they like to try and push automatic software installations along with security updates (I am looking at you IE8 and probably IE9 a few years from now).
Stark can probably add some more pointers from his time as IT.
