Stay away from PCI Express, some of the items are in your budget but most are not.
Here is my version of the perfect working mans computer that will support your needs.
Antec case with Antec true power 550watt(make sure you get the one with front fan) $157.00
ASUS P4C800-E deluxe Prescott ready motherboard. $179
ASUS Ax 800Pro/TVD 256mb AGP video card. $549
Intel P4 3.2ghz 1mb cache hyper thread Prescott CPU. $215
Dual Western Digital 160gb hard drives. $280
Sony or such floppy drive. $8
Sony CD/RW and DVD/RW drives (separate and do not use their software). $200
Vantec Fan card (for the vid card). $20
2 Corsair 1GB 3200 400 XMS Ram memory. $320
Monitor, keyboard, mouse, printer and scanner varies on what your exact use is. The peripherals alone could cost you $2500.
Lets say you go with a 17" LCD monitor, standard keyboard and mouse, and a printer/scanner combo. $600
$2528 Total without taxes/shipping
Now this is a rough price and has no OS or Office program.
This system will do all of your Adobe video stuff, no problem.
As you see, you need a big vid card and lots of ram/hard drive space.
Hope that helps,
Your Hardware Guide.