Well, you can have the Asrock 939 Dual mobo, this supports BOTH AGP AND PCI-E I personally am running this smoothly with an Amd 3000 and Crcuail 2x512mb Ram.
1gb is enough really, are you gaming? What you doing, with it ?
YOU DONT NEED A 64BIT OS, I DON'T Personally, not enough programs...