XPS 720 can't take 2x2 Dominator PC2-8500 ram!!! Chris_M, need some DELL official information.

My XPS 720 is currently struggling with Corsair 4GB dominator PC2-8500 Kit under EPP/SLI ram support ON in BIOS. the system randomly reboot and locked up. 
I have the mobo replaced twice, and the issue was still out there. (the ram kit was fully tested with no error).

I emailed the tech. support for some error code i received, and here is the reply:
=========================================================================
I did some research with the error messages that you are encountering. 
 gathered this could be related to the Corsair Memory Kit that you have on your computer. 
This could also be due to the compatibility issues between the Corsair Memory and your motherboard 
as your motherboard can only support 2GB of Corsair Memory matched pair of DDR2 SDRAM DIMMs.
=========================================================================

I'm curious if the xps 720 only can support 4X1G dominator in the system, BUT no support for 2X2G dominator kit. ps, before upgrading to Dominator 4G (2x2G), 
they system was rock solid with Corsair DDR2-800 CL5 DHX 4GB (2X2G) KIT. 

Some helps, please!