756MB of RAM on a 1.4ghz Athlon is not a shortcoming.

I'd say about the only thing you might find worth doing with that rig on cost/benefit would be upgrade the graphics card to a low end directx9 card.

Something like a X1300 should give a big 3d performance increase over a GF4MX without blowing the budget & without either leaving the CPU as bottleneck or killing the PSU.