Windows XP reporting incorrect memory information

Hi,
I just purchased a new PC, with 4GB of RAM, running XP Media Center 2005
SP2. I noticed it swapping quite a bit while gaming, so I checked the system
properties and it only reports 1.75GB of RAM, with PAE automatically enabled.
When I look at System Information (msinfo32), it shows 4GB of installed RAM,
2 GB of Physical RAM, 2 GB of Virtual RAM and then my page file (4GB). The
memory stats in task manager seem to confirm that it's only utilizing
1.75-2GB of the RAM. Is this a limitation of Media Center Edition? The PC
it replaced also had 4GB of RAM, reported as 3+GB (as it should), but it was
running XP Pro SP2.

I'm stumped. Any thoughts on why it's not seeing all of the RAM as physical
memory and/or how to fix it?