Need New Motherboard That Supports 4+GB Memory. Help!

Please help. I've looked at all the manufacturer sites and can't get an answer. Right now I'm running an Asus P5AD2-E Premium motherboard with Pentium 4 670, 4GB RAM, and Windows Vista 64-bit. My motherboard and Windows only show 3.2GB. 64-bit Windows is supposed to fix this but it didn't. Seeing as my motherboard won't show it all, I'm blaming that, and Asus has been unsuccessful in helping me. They obviously don't know their own BIOS' because mine doesn't offer any sort of memory re-mapping feature. I also called Gigabyte about their GA-P965-DS3 and he doesn't think it will show all 4096MB either, but said it will still be able to use it...doesn't make sense to me. Can someone please tell me some overclockable motherboards, inexpensive, that support Pentium 4 (although I may get a Pentium D or entry Core 2 Duo) and 4 x 1GB DDR2 533MHz non-ECC DIMMs? Thanks.