Memory Usage

Hello, this is my first time posting to one of these message boards, so please bare with me. I have an HP DV6605US Laptop, which I have expanded the memory to 4gigs. I got a nasty virus after trying to download a bootleged copy of Nero 9, so I lost my Windows Vista Home Premium Edition. I am currently running Windows Vista Ultimate 32 bit. I just recently installed Vista Service Pack 2 and my memory usage has skyrocketed. Prior to the install my processor would be running at maybe 2 or 3 percent and my memory usage would be at 40 percent tops, usually around 30 percent. Since the install, my cpu percentage is still the same but my memory usage has risen to 87 percent! How do I lower my memory usage? Should I upgrade to 64 bit Vista Ultimate? Or should I wait to get Windows 7 Ultimate from expertzone?