Windows RAM problem

[Cobrajet33089]

I know that in a Windows XP system, the maximum supported RAM is 4GB last I heard, however this can often be limited to only matched pairs of RAM. Recenlty I installed 4GB of Corsair XMS2 in a clients computer only to have 2.5GB show up in the System information section. I have tested each stick individually and 1GB shows up for each when installed seperately, however when more that 2 sticks are installed it limits to 2.5GB. I have tried aranging them in various pairing configurations, and double checked the serial numbers verifying that the last three digits lay in the folloing order 041,042,043,044. I have no idea what the problem is, the Mother board is a M2N32-SLI Deluxe, I sent the machine to my client and told him I would let him know when I found a solution for the problem, but the machine, as best I can tell, appears to be utilizing all 4GB per the 3DMark benchmarks, and MemMax test but I cant get Windows to recognize it.. I would appreciate some more info on a possible fix if anyone else has seen a problem like this before. Thanks everyone!

[Lissyx]

I have a Abit AN7 mobo, and manual specifies that it supports at least 3GB of DDR333 memory or 2GB of DDR400.

And, both Windows and Debian see correctly my 3GB

So, maybe it's a mobo issue ?