Budget system:CPU vs video card

Not actually building one right now, but just suppose building a budget system with a low end Athlon XP and low end video ($60-$75). Where would money be better spent performance-wise:a CPU upgrade, say from a XP1800 to XP2000, or a video card upgrade.
I know it’s a somewhat subjective question, so I’ll spread points to 2 or 3 best thought out answers.