Tech support advice request...?

Greetings, I have been using Windows XP x64 since it's release but due to a hardware issue with my motherboard (it's built in NIC died) I am forced to revert to Windows XP x86. Since I built my computer for x64 it has eight gigabytes of DDR 800 RAM. Windows XP x86 can only use three gigabytes so the other five are in limbo. What I wonder is if there is a utility that can run before Windows loads that could reserve this five gigabytes as a RAM disk which XP could then use? (Yes, I could buy another motherboard and I could even RMA this one but I decided to not RMA because this IS an RAM replacement - the fourth- and I decided to wait to buy another so I can get the AM2/AM2+ so I have upgrade options later.) Any help with links would be appreciated.