2005? Multiple things wrong with it? How many capacitors on the motherboard look like
this?
Prerequisite questions:
- Are you planning on reusing any parts from your existing computer (optical drives, case, etc)? If you plan on reusing the case, is it ATX or MicroATX?
- What's your budget?
I recommend an i5 2500 over the Phenom II X6. Despite it having two fewer cores, it benchmarks a good deal higher (in everything except highly threaded rendering and scientific applications) and only costs $20 more.
You can build a machine with an i5 2500k, Z68 motherboard, 8 gigs of RAM, a 1 gig Radeon HD 6870, a pair of 500 gig Caviar Black drives for a RAID 1 boot volume, and Windows 7 Home Premium for about 900 bucks. You'll get the best price/performance result Intel currently has to offer, overclocking, the ability to switch between the video card and onboard graphics (more power savings, less heat, and you can use Quick Sync for video encoding), and you'll still have 2 empty RAM slots and the ability to eventually drop in a second 6870 for Crossfire as an upgrade.
If you don't need that much, swapping the above parts for an i5 2400, H67 motherboard, 8 gigs of more appropriate RAM, and Radeon HD 6770 gets you down to under $750. You don't get the ability to overclock or use dual video cards, but you still get a really stout processor (which still beats that Phenom by a good margin except for POV-Ray and heavily threaded scientific software, this time for practically the same price) and plenty of memory.
In both theoretical builds, the two hard drives are $50 apiece, and I'm figuring in $50 for a decent case. You can easily save some money if you have a case to reuse, and you could always go with one hard drive. (Personally I like the safety of a mirrored boot volume, and Western Digital gives you a 5 year warranty with the Black line.)
If you or someone you know is in college, you can knock that Windows license cost down a bit, too.