I have a similar problem
I have 1gb+1gb of Ram and want to upgrade to 2gb+2gb ram.
If I install the new RAM I get the one short, one long beep from the bios indicating a ram error.
If I install 1+2 or 2+1, or 2+2 I get the beeps. I go back to 1+1 and its fine.
The specs say it can take 2+2 gb...