My dream machine... hmmm. In semi-general terms:

Antec SX1480B server cube case with built-in coffeemaker
Dual AthlonMP processors
Tyan Thunder K7 motherboard, or something similar with more tweakability
3Gb DDR RAM (I hit a peak memory usage of over 1600Mb the other day... half of it being virtual memory )

Ultra160 SCSI RAID5 with those new Seagate Cheetah X15-36LP's
DVD-RAM drive
CD-R/RW drive
CD-ROM drive
Three 3.5" floppys in RAID5 (ok, not really )

ELSA GLoria DCC primary video card
ELSA Gladiac 511PCI secondary (dual-monitor)
Three 18.1" Planar LCD monitors and a real big desk

Creative Labs SBLive or something
Wireless headphone setup
3Com 3CR996-T 10/100/1000 NIC

IBM click-clack keyboard
Microsoft Intellimouse Explorer
Wacom Intuious 12" x 9"graphics tablet
Microsoft Win2k Pro/Win98SE dual boot
Microsoft Office XP
Caligari trueSpace 5
Discreet 3D Studio Max
Microsoft SoftImage
Newtek Lightwave 3D 5.5 (now you see why I want all that RAM)

That would be a great setup for some 3D modelling, which is a hobby of mine. I have a dual-P3 733 that's been calculating radiosity for the last 14 hours in trueSpace 4.3, and it's only 40% done, so I'd love to have a dual-AthlonMP to speed this up a bit.