Can I run a 256 MB module in my Dimm A slot and a 128 MB module in my DimM B slot or do they both have to be the same (MB 128 and 128 or 256 and 256)?

That depends on the hardware. Some machines required matched pairs of ram, others don't. If it's that same machine we were discussing, you should ask Dell, as they'd be able to tell you.

I just grabbed your manual online from Dell, and it doesn't say, wish I could give you an answer, but you'll be best off if you call Dell and ask them. Sorry the manual didn't say anymore than how to install the memory. :(

just put them both in and see if it will post/start. if it doesnt take the 128 out.

commented: makes sense to me, that's what I would have tried/suggested. +1
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