Dell Dimension 9200 (DXP061) - XP Pre-load recognizes only 3 GB of RAM; BIOS detects 4 GB

I have brand new Dimension 9200 (DXP061) machines (3 pieces).
The machines are default configuration with a 256MB ATI Radeon X1300 Pro card pre-assembled.
Before ordering more than the 2 GB (2x 1 GB modules) RAM, I tried to see how one of them would run when filled up when adding 2x 1GB from one of the other machines.
 
According to the docs, these machines should be able to accept 4x 1GB modules
http://support.euro.dell.com/support/edocs/systems/dim9200/en/SM_EN/specs.htm
 
In fact the BIOS (latest version, 2.0.5) does recognize it.
However, when booting the preloaded Windows XP, it only recognizes 3 gigabytes.
 
I'd expect Windows XP to recognize roughly 3.5 gigabyte of memory (so it can reserve address space for the PCI memory mapped video card: the 256MB ATI Radeon X1300 Pro).
 
What should I do to get XP to recognize more memory?
 
Regards,
 
--jeroen

Message Edited by jeroenp on 12-27-200610:49 AM