850? Definatly, now I'm not sure what Fry's is, but I'll go out on a limb and assume it's like a Comp-USA, a big building full of everything computer.
Places like these (or at least Comp-USA) often have sales so it's best not to look for specific brand's, but rather something on sale that fits the bill (and slot!).
For gaming, as always, we want AMD. Now this is very important, do
not get an Athlon - XP, get an Athlon - 64. Some salesmen might try and push an XP on you because they've got a lot of them in stock, but don't buy it, it is honestly inferior.
Ihonestly don't know the difference between the 939 pin and the other (754 perhaps, I can't remeber). Just make sure that whatever you get, it fits the MB, you'll feel pretty stupid if your processor doesn't fit into your MB.
I think a 3400+ is in your pricerange.
RAM
As for Ram, get whatever the motherboard can support, pc3200 is the standard, as I recall. PC2700 is a bit slower, again, I don't know how much of a difference you'll see; just get a gig of it, that's the important part. If you can get something fancy like Kingston or Corsair, that'd be cool, but you can always get something less expensive that's just as good, micron or crucial or whatever, there are a lot of names, those are the big ones I know of. Just make sure it has the right number of pins for your MB, again.
Do whatever you have to in order to get 1 gig of it, though. It should be within your price range.
For video card, I happen to like the ATI's myself, something from the 9800 family works, they've got a half dozen of them, some have 256megs of ram, some have 128, go with whatever you can afford really, everything is 8x AGP these days, but make sure, don't let them sell you a PCI graphics card or something wierd like that.
They are something like 125-225, get whatever from that family that you can afford.
Sound Card
Your MB might possibly have a decent sound card built in, but if you want sorround sound you'll prolly have to go with an extra card - Creative Labs makes fine stuff for good prices, though in this department I know very little, so I'd just get whatever you can afford (hell they even sell USB sound card's these days).
These can be like 50 bucks, up to you.
Power Supply
I've always felt 420watts was a good number, but again, see what's there; I wouldn't go under 350watts however. Though chances are it might just come with the case you buy
Heh, you'll need one of these, so work it into the budget
Case
It doesn't matter, I'd suggest not getting one of those flashy ones with the plastic see through side panels, they don't hold up as well, get something nice and sturdy; and make sure your MB will fit of course.
Again, needed; figure it out. Also, make sure you have the tools to install it (screw driver... I'm almost positive the MB comes with screws).
HD:
Maxtor, Seagate, whatever, not a big deal here, 7200rpm is standard, ATA-100 or 133, no major difference for games as far as I know. Buy at least 80 gigs
Purchase according to how much you can pay for.
OS
I'd get XP professional, but that's up to you. For games, I wouldn't go linux.
You could try to get a student version, it's cheaper, but in the end, you'll need XP if you wanna play HL2
Optical Drive:
Ya.. you don't want to forget a DVD-Rom drive, these days the big thing is the DVD/CD-RW combo drives, but that depends on if you plan on burning stuff. Just as a note, CD-RW's are far more versitile than CD-R's, I use the suckers like I did floppies. Just, you know, make sure it's not slow as shit.
These things are pretty cheap, but I'd definatly go DVD-rom over just CD-rom, as more and more games are dvd's these days.
Cooling:
MAKE SURE your processor has a fan and a heat sink, some come with, some don't. If it doesn't, make sure to buy a fan/sink that'll fit and some of the special adhesive to glue it on.
Get at least 2 fans for the computer itself, 1 in, 1 out. Make sure your case will support these fans too. Oh and makes sure the
Fans are cheap as hell.
Edit - Did I mention that I have an AMD/ATI bias? I do, I'm sure the Nvidia cards are just fine, honestly, if you see an Nvidia of similar price, I'm sure it'll work out just fine - same with Intel MB/CPU.