I am planning on upgrading my laptop's RAM, and it says that the maximum supported memory is 2x512mb in each slot. My video card uses up 128mb of that ram, so it will actually be less than 1gb. I am wondering, can I put 1gb of memory in one slot and leave an already installed 256mb ram in the other? It says it supports only 512mb in each slot. Does that mean it can't run a 1gb in one slot?