Here is a selection of games I have tried on my macbook 1.8ghz with 1Gb ram, all memory split evenly between osx and xp, and parallels running with added importance over osx.
Command And Conquer Red Alert 1 (DX 3) - 256 colour, frame rate fine but colours make it unplayable.
Theme Hospital (DX 4/5) 16 colour, frame rate great but colours make it unplayable.
Railroad Tycoon 2 (DX 8.1), rubbish 256 colour problem again.
Chris Sawyers Locomotion (DX 9b) 256 colour, frame rate great but colours make it unplayable.
So all in all it was a pretty rubbish experience, all the games were working in very low colour which made them unplayable