Windows 7 and 4GB RAM

WARNING: Long post ahead!

I tried the beta of Windows 7 x64 back in January on my main PC, set up in a dual-boot scenario with Windows XP SP3 x86 (my main OS). It worked well, and I used it for a couple of days.

I purchased 4GB of 2x2GB Dual Channel RAM (Corsair brand), since XP was always sluggish even on 1GB. After installing the two modules, I was unable to start Windows 7. Windows XP never complained (although since it is 32-bit, it only reports 3.25GB of RAM installed). It complained "The bios in this system is not fully ACPI compliant".