you can build a pretty sick system with 3k. i suggest going to newegg.com and doing a little research. here's one system i concocted for under $1500:
1 lite-on combo drive (23.99)
1 lg 20x dvd burner (24.99)
antec 900 case (129.99)
2x 250gb seagate barracuda sata 3gb/s hard drives (119.98 or 59.99 each)
lg 22" widescreen monitor (279.99)
asrock am2+/am2 nforce 780i motherboard (189.99)
2x evga geforce 8800gt video cards for sli (299.98 or 149.99 each)
corsair 750w power supply (129.99)
4gb (2x2gb) mushkin ddr2 800 ram (93.98 or 46.99 for 2 gigs)
amd athlon 64 x2 6000+ 3ghz socket am2 processor (92.99)
it comes out to a little over $1400 after shipping. but don't just take this build and do it. do some research for yourself, determine whether or not you like amd or intel, ati or nvidia, etc. and if this build tickles your fancy, then go with it. good luck!