Vista - Can't install Vista Business unless I downgrade RAM from 4x512 to 2x512

Hello all. This is my first post. I have been searching everywhere for a resolution, but so far, cannot find one. I have run Windows XP on my system since 2004. I have been running 2GB of system RAM through 4x512 Corsair valueselect memory sticks. I attempted to install Vista Business on Monday and the system would never get to the point where it would ask to create the user account without going into a reboot loop that I couldn't get out of (even in safe mode). After removing and replacing hardware, the only thing that would solve the problem was to remove 2 of the 512 sticks and leaving the RAM at 1GB. Now after vista is installed, I can't put the RAM back without having the reboot loop return.

Does know how I can get Vista to recognize my other 1GB without getting all mad and throwing a temper tantrum?

System is:

Abit Av8
Athlon Dual Core 4400+
Corsair value select 4x512
ATI 2600XT PRO
X-Fi Xtremegamer
Pioneer DVD Burner
Lite ON blu ray drive
Hauppague HVR 1600

Subscribed. I have Vista 64 bit Home Premium and I conducted the first reformat since I built the box 20 months ago (ran flawless before.) When the format was done installing the new files the system turned off and would attempt to finish the format while launching windows. This is where I see a blue screen flash with a Memory Dump message, but it goes away after a few seconds.

I have 4x 1GB Corsair XMS DDR2 of memory in the system. The format finished without issues when I took out 2x 1GB sticks leaving 2GB and 2 of the 4 memory slots in use. Initially after the format I ran some updates and rebooted without issues. Now about 2 days later I cannot boot the system into windows with 4 GB of memory or I get the same blue screen message.

-Karl