Octopus Overlords

I've been out of the upgrade race for a couple of years now, and I'm still running along with an old Athlon XP 1800, with a Geforce 3. Work is offering me up a new position, which will come with a substantial increase in pay. The situation finally allows me to justify spending a substantial bit of money to upgrade my gaming rig. The problem is, I've been out of the gaming loop for so long, that I'm not sure where best to spend my money, and what offers the best bang for my buck.

I'd like to be able to, at a minimum, play the newest breed of shooters, without spending too much money. I'll probably have about $600-1000 to spend over the next month or two.

I've got a great monitor and a decent DVD/CD-R burner, etc. I'm mainly interested in purchasing the following components:

Hard Drive(100-160GB)
Mobo
CPU(prefer AMD, but is the XP ok, or should I go with the 64)
RAM
Video Card
Sound Card
a new case

I'm trying to look through Pricewatch at the moment, but I'm feeling totally loss.

Thanks for your help, I really want to play HL2!

Well, I'm new around these parts here, but I've recently just built my own rig and spent about $625 on the following parts. I just picked up doom 3 and can run it on high quality with just a little stutter, so what I've read about HL2 means that I should be able to run it with quite a few bells and whistles.

CPU-AMD Athlon 64 3200 socket 754-running around $200 right now.
Mobo-MSI k8n neo platinum nforce 3 250 gb chipset-$125
hard drive-maxtor 120 gig 7200 rpm ide-about $90.
ram-corsair value ddr 3200-about $80 for 512 mb stick.
thermaltake tsunami series va300 w/400 psu-about $130.

I already had an ati 9800 pro and monitor. I'm just using on-board sound.
Those vid cards can be found for about $200. I wanted to get the dfi lanparty motherboard since everyone's raving about it's overclocking abilities, but I couldn't wait for someone to get it in stock. Those boards seem to by flying out the door.

With those parts mentioned, price is $825. However, you could definitely shave off some $ by getting a different case, probably an Antec case, for $30 to $50 less. Or if you're not in a hurry to build, wait for socket 939 athlon 64 chips to come down in price since that's where amd looks to be headed for chipset design in the future and the life-span of your rig will last a bit longer.

I could keep going on, but I won't. By the way this was a first time build for me and I had it up and running in an afternoon. I bought everything in a retail box just so I could have manuals with everything. If you know what you're doing you could buy OEM parts and save some cash there as well.

Oh, and I bought everything from newegg. To me, it's just a lot easier to shop there and if I had problems, I knew where to go and what to do about it with them.

Mental note to self- use preview button before posting...