Yes, not toooo much though. As example, i have 2gb (ddr2)RAM, vista uses <30% of it in idle, that makes ~614 mb. By using the vista basis design/anything but aero, the RAM usage drops by <5%, that makes ~512 mb (which kinda makes me wonder how your pc can handle it ^^"). Also your gfx card/chip won´t have to bother doing the 3d interface/transparence stuff anymore.
So theoretically, this could help a little. Still, try to update you gfx drivers by downloading them from the official site of the company that developed your card/chip, since doing it with windows update sucks because of the driver versions they offer.... And you are right about the ram upgrade imo.