Greetings Ryan,

I have tested and experimented different setups under XP and Vista.

Here's what I would buy today, starting from scratch, in order of priority.
Or recommand to a friend starting to multi-box.

1. An Intel QUAD core 6600 (a 6850 DUO core really suffers when you multi-box, for a similar retail price as a Quad).
Plus you can easily overclock it to 3.0ghz through Bios.

2. A GFX card with 512 mo ram (256 isn't enough for sure and 312 is barely coping).
Get a Nvidia 8800GT or an ATI 3870 with 512mo, based on what you favor as a GFX brand.

3. At least 3Go of system Ram (by far the cheapest component to upgrade from 2Go anyway).

4. A case with 500watts power supply, 650watts offering a safer margin.

This should easily come below your USD 1,000 max budget.

Note : with this setup, I can get 30 FPS on my main and 40-60fps on my alts. Pretty comfortable for multi-boxing.

/salute