Have exactly this problem and was hoping to see a solution but I see this post was middle of last year and has not seen any answers. I have parallels 3.0 build 5582 running XP SP2 in VM on Leopard 10.5.1 and its driving me nuts. As soon as I full screen parallels it starts in a lower resolution, I reset it to 1440 x 900 and its great. However, once I go back to the smaller windw then jump back to the full screen its lost the damn setting again. Never did this with 2.0 on Tiger