definately a larger hard drive, as u might not find a 40GB available as a new hard drive.
and get wither ATi Radeon 9800 PRO 128MB version (not PRO with 256MB)
or, get 9800XT. (9800PRO with 256MB is slower than both 128MB in PRO and XT is of course faster.)
and BEST is to get some good manufacturer in motherboard. Asus A7N8X is award winning AMD Athlon Flagship, and I'll recommend it eyes shut.