I'm looking to drop some money into my computer. Need help!

I'm both a console and pc gamer, and as much as i'd love to buy more games for pc, my rig can't run at high enough settings to compare to my 360, so i stick to consoles more. but now that i recently got a job, i'm looking to put some money into my computer. my question is, should i completely scrap what i have now and rebuild, or use what i have and upgrade? my comp i have now was built from scratch in 2002 or 2003, i don't remember, but i've added ram and a video card over the past year. on my current rig i have 2 gigs of ram, my cpu is only at 2.67Ghz, motherboard is PCI, and my video card is an ATI Radeon x1600 Pro. lol do i need to tell anymore additional information? and to add to what i'm aiming for, i would like to play games like The Witcher, Crysis, Quake Wars, Spore, Loki, Hellgate, and the Medieval 2 seriesall at very high, and possibly max setting. thanks alot for any help or feedback i get. i really appreciate it.

Ok, uhm i dont know much about computers, so i'll take a shot in the dark to answer that haha. It's an Intel 4 cpu with 2.67 Ghz, motherboard is PCI-E. what else did you want to know?

This is tough, lol. You're computer probably doesn't support core 2 duo seeing as it's slightly older, but you could probably overclock the CPU if necessary.

For a graphics card, I would go for something along the lines of THIS.

Apart from CPU, RAM, and video card, there's not much upgrading needed for computers. You already have a fairly decent processor (which could be overclocked, although you'd need better cooling), 2 gigs of ram, all you need is a nicer video card.

Edit: I'm no computer master, but I think there are programs that tell you what you're hardware is and stuff. If you find out your CPUs front side bus and socket type, we could tell you of upgrades.