Gfx upgrade or cpu uprgade...

[-=arif=-]

Hello, not sure if I should post this in the cpu or the gfx section, so here goes..
Have myself a Shuttle SN21G5, Athlon3500venice, Pcolor X800GT, 1gb ram(single)
Out of the following 2, what would give me the most improvement in terms of playing games and watching hd video:
changing the cpu to athlon 4000 single core
or
changing the gfx card to a X1950pro/7900gt

Help and advice much appreciated.

 

[-=arif=-]

thanks for the advice fellas, stick and x1950pro...here I come!