Diablo 2 doesn't work with Intel graphics on the Macbooks and Mini's that have them (950 and x3100).
You'll have to wait for the 1.13 patch, which is in beta testing now. 1.13 fixes this issue.
Apple removed 256 color modes and it hosed a bunch of games for Intel Graphics users. Starcraft was fixed already and the Diablo 2 patch is taking forever to get out the door.
I think this has been broken for over year and half.
Nvidia and ATI GPU's are fine though.