Case: Lian-Li PC-61+USB (Black) = $155
Power: Enlight ATX 340W = $38
CPU: AMD ATHLON XP 2100+ = $241
Mobo: MSI KT3 ULTRA-ARU KT333 = $128
RAM: 2x KINGSTON 512MB PC2700 DDR RAM = $338 (2 x 169)
Video: Asus V8460 Geforce 4 Ti 4600 = $386
HD: WESTERN DIGITAL "SPECIAL EDITION" 100GB 7200RPM = $183
Sound: Sound Blaster Audigy Platinum = $166
CD-RW: PLEXTOR 24x10x40 CD-RW BLACK = $132
DVD: Lite-On 16x DVD Black = $55
Floppy: Panasonic Black = $12
Keyboard: BLACK ORtek = $12
Mouse: Pine Group Optical Scroll mouse = $8
Total = $1854
+ shipping ($48)
Total w/ shipping = $1902 (newegg.com)
If you absolutly cant go above $1800, there is PLENTY of stuff to trim from this system to get it there... if you already have a CD-RW/DVD/Floppy/Mouse/Keyboard... theres a big chunk of money right there. Other things you can cut are the SB Platinum, and the 100gb 8mb buffer HD. I would leave the 2100+, 1gb PC2700, and GF4 tho... cause those are really gonna be the basis of your computer.
Anyway, good luck!