I've learned that there is no perfect AGP motherboard but the Conroe865PE is very close to it. It has good W7 support (no AGP issues) and supports up to the QX6800 (Im using a QX6700 ATM).
There are two drawbacks: 1)due to a chipset limitation, W7 won't recognize more than 3520MB of RAM; there's not enough registries in the chipset to handle above that amount, which makes sense as we're talking about a 10 year old chipset. 2) when using a 1066Mhz CPU the RAM divider is set at 3:2 no matter what you select in the bios so my DDR500 RAM is running at 177Mhz (DDR354). There's a modded 1:1 and 5:4 bios but I haven't been able to find it (there's tons of links on goggle but all of them lead to the same forum but the thread has been removed).
I'm trying to mod the bios myself but I've got too much to read
Another good option is the 4CoreDual-VSTA/SATA2 (both are the same board but the SATA2 has SATA2 ports obviously) as they support DDR2 meaning faster RAM BUT they have the same chipset RAM limitation as the 865PE chipset and you have to use a modded bios (this one is still available) to be able to use 2GB DDR2 sticks.
Still, the AM2NF3-VSTA is quite a feat too (Phenom II support out of an NF3 board
) , and I think that there are Vista drivers for it so you could try that too.