I am using Vista 32bit home basic and i think i can use 4GB. So far i have 3.25GB of ram, one stick of 256mb DDR2 and 3 sticks of 3GB's of ddr2. Everything is working great, the OS is lovely, games are running amazing on my rig(with PCI cards), even tho i am moving on to PCIE soon, because i have a full x16 slot, etc. Speed is great, etc. So i was curious is it worth the upgrade to 64Bit or just stick with Vista 32bit? I am very temp to upgrade, its like i can't stop thinking about it hahaha.