All completely valid -- I'm using a quad-core processor (not sure about the memory channels) -- but I'm running 64-bit vista and I installed the x64 version of gimp. However, I'm thinking that something is going on akin to what you're describing, because last night I was running gimp and doing a bunch of other stuff, and using the same ratio of resources (and everything was alot slower). It's my first multi-core processor and I'm new to vista from 32-bit xp, so maybe I have something set wrong >.<