YEP, first place to put your money should be on a new gfx card, GF3 ($90), Rad8500 ($100) or GF4TI4200 ($150) are your best choices, the 4200 is clearly the best option, the others are fine if you HAVE to skimp, but the gfx card is the WORST place to skimp for gaming perf. You really want a 128MB gfx card whatever gfx card you choose, 64MB is already limiting in some games, and this will definitely become more pronounced. When it comes to selling your 128MB gfx card, it will sell FAR better than a 64MB card, just see how many people currently want a 32MB card! Even with your current 1ghz CPU, you will still get a big gain in perf and can still tap the unsed GPU power by enabling AA & Aniso as well as cranking up the res.
As for CPU, mobo and RAM, are you interested in o/c'ing or onboard functions, what's your budget? Whether you go P4 or AthlonXP you really should get DDR RAM and not RIMM.
RIMM vs DDR, IMHO DDR is the wiser choice at the moment but I wouldn't suggest changing your mobo just to use it. DDR333 is easily on par with RIMM-PC800 and isn't far behind RIMM-PC1066, just check out both prices and availability! I believe Intel are doing a U-turn (albeit on the quiet) and now realise that DDR is currently the way to go. Intel P4 RIMM mobos don't use the ICH4 southbridge (IIRC USB2, AGP8x, ATA133 etc), they use the older ICH2. Intel P4 DDR mobos use ICH4 and it's well worth having for the future while Intel RIMM mobos are NOT certified to use ICH4. Of course USB2 can easily be added via PCI and ATA133 & AGP8x are more to do with marketing than performance at the moment, but I think the ICH factor does show Intel's quiet preference for DDR along with Intel's investament into dual cahnnel DDR. With RIMM being expensive and PC1066 rare AND with DDR400 and dual channel DDR on the horizon (not like nForce's shabby implimentation which only boosted the onboard GF2MX gfx), DDR is looking the better technology. Well in the case of upgradability and flexibility for RIMM you
can just add 1 RDRAM (RIMM/RAMBUS) module but you will need to put a CRIMM (Continuity module) in the next vacant slot. Bear in mind this will severely effect the RAM throughput of your PC from 1600MB/s to 800MB/s, so basicly you have to use PAIRS! DDR has no such limitations and works out much more economical and flexible when buying or upgrading RAM. DDR also o/c's far better than RIMM and is certainly more flexible and able to run very well async to the FSB, often RIMM becomes the limiting factor when o/c'ing. RIMM isn't dead nor poor perf-wise by any means, but if it was my money I'd spend it on DDR.
Here's some useful links:
DDR vs RIMM:
http://www17.tomshardware.com/mainboard/02q2/020501/index.html
DDR vs RIMM:
http://www.xbitlabs.com/mainboards/i845g-i845e/
Intel mobos using DDR:
http://www17.tomshardware.com/mainboard/02q2/020520/index.html
VIA P4 mobos using DDR:
http://www17.tomshardware.com/mainboard/02q2/020514/index.html
SiS P4 DDR333 mobos:
http://www17.tomshardware.com/mainboard/02q2/020403/index.html
Intel 845 mobos vs the rest:
http://www.xbitlabs.com/mainboards/i845g-i845gl/
P4 SiS645DX and sneak peak at DDR400:
http://www.xbitlabs.com/mainboards/sis645dx/
P4 mobos compared:
http://www.xbitlabs.com/mainboards/p4-chipsets-comparison/
Specifics on mobo (in this case P4 Skt423/478):
http://www17.tomshardware.com/mainboard/02q2/020422/chipset-07.html
TR Chipset reviews:
http://www.tech-report.com/reviews/chipsets.x
TR Mobo reviews:
http://www.tech-report.com/reviews/motherboards.x
Firing Squad (scroll to mobo section and check for 2002 dates):
http://firingsquad.gamers.com/hardware/