Asus A7N8X Motherboard $78.00
AMD Athlon XP Mobile 2500+ $79.50
Thermaltake Volcano 10+ HS/Fan $28.99
Mushkin 512MB PC3200 DDR $74.74 x 2 if fits budget
Maxtor 80GB ATA133 8MB Hard Drive $68.00

That's only $400 if you go with 2 sticks of 512mb. That leaves you with a good bit for a quality video card. I'm sure your company won't mind you spending around 5-600 if they were going to give you a company PC anyway.

I suck at video cards so I'll let someone else suggest that. h: