I can’t tell you. But what I can suggest is that your motherboard manual might not exactly be lying, but not telling you that the “maximum” RAM you can fit is in fact just what was available at the time, not the maximum. I’ve just looked at a PC that had 512MB of RAM already. The manual said “2GB max” (2 x 1GB sticks); however the local PC guy only had 1GB available but said he’d be happy for me to try a 2GB stick and then return it if it didn’t work. However it did work just fine, so the PC now has just under 2.5GB of RAM and is running much faster.
Apparently, when these manuals get written they may only have access to say 1GB sticks so they put this as the “maximum”, when what they mean is this was all they could test with.
Also, don’t assume this will work with Dell PCs as they can be funny; I’ve just seen a Dell that really did refuse to switch on Dual Channel mode unless both RAM sticks matched in size (it would just opt for the larger of the two if there was a mismatch) and then had to fight it to clock 800MHz RAM down to 533 (the trick is to fit one 533MHz stick and one 800MHz stick; the faster RAM seems to clock down automatically and swithces dual-channel mode on so you get the benefit of the full capacity).