I can vouch that 10.2 runs smoothly on those exact specs, but 10.4, not so much. Our pismo runs 9 and loves it. If the G3 inside is anything like the imac g3's then 10.3 would run O.K. on there as well. tiger is a hog, but if you can get 512-1gb ram in there then it will be much better. tiger on a g4 350 is very nice with 1gb so I imagine the same for the pismo.