is that $3k US, Aussie, Canadian?
CPU: I'd say Athlon 64 3400+
the main reason I like it better is not because it does 64-bit (but that is still part of the reason) it is mainly because it can outperform the P4 extreme, and at half its price!
mobo: Asus K8V Deluxe socket 754
Radeon 9800XT 256MB - bundled with HL2 voucher
extremely good video card, definately enough memory for games like HL2 or Doom III
160GB SATA SEAGATE
and maybe an SCSI controller with a 36GB SCSI SEAGATE HDD to put your OS's and Program Files on, will free up the use (I mean access, not size, but it still does save size) of your 160GB HDD so all its use will go to your games and such
I like Seagate for being less expensive, extremely high quality, and virtually silent
monitor: look for a 21" at a swap meet (one that you see operating so you know it works) for a low $
ive seen a Sony Trinitron 21" for like $400 AUS (roughly $250-300 US) at one, and they had it operating, it really did look good
speakers: Logitech X-620 6.1 not too expensive but very good