hmm, if it is for gaming, I would suggest something like this:
E6600 ($350)
Nforce 590 or 975X motherboard (about $250) depending on your GPU preference
2x1GB DDR2 800 (you could go higher, but i don't think you will NEED it, but if you have extra money to burn, then go for faster mem, corsair, crucial, OCZ platinum would all be fine) (about $250)
whatever hard drives you want (say $200 for a basic RAID setup or a raptor system drive and a bigger storage drive)
Optical drive (about $30)
2x 7900 GT[X if you can afford it] or 2x1900 XT (one crossfire edition) ($750)
Case and PSU ($250). personally, I personally like aluminum full towers like the thermaltake armor, but I also stick with air cooling, so make sure whatever you go with will fit your water system.
all together, that is about $2050, but my estimates are also a bit on the high side. you would have to provide your own mouse, keyboard and monitor. You could also save a ton of money by sticking to a single videocard solution. but you really want the best gaming experience, dual-card does over much better performance (just not much value IMO). Also, you could stick with a single hard drive for now, and save a bunch more.
all in all, $2000 is more than enough for a very high end system, much more system than most people really need. so decide if you want to spend all the way up to your budget, or if you would rather sacrifice a bit of performance for a bit more cash in your pocket...