I have a 2004-generation XPS with 4 memory slots.  Slots 1 and 2 each have 512 cards.  If I upgrade to at least 3GB memory, can I mix the 512 slots with 2 1GB cards?  I would assume no, but some genius at Fry's seems to think so.  I'm not doing anything until I hear from my "brain" trust.

Thanks.