Your really stupid.
Sorry to go off topic, but I have to learn this guy something...
We don't know "what" your computer's resources are (as it's really hard to define such a thing), but we DO know that EVERY program that runs on your computer uses up resources. Especially things like WindowsBlinds that leave the Windows GUI on (which uses a fair amount of resources) then overlaps it with your custom one (which uses a high amount of resources). Therefore, by running WindowsBlinds, your almost doubling the resources your system theme uses. The more resources 1 program uses, the slower all the others go. Your computer only has so many usable resources, and if it runs out, your screwed deep.
Now if you think i'm lying, do this:
Run WindowsBlinds, then open up Photoshop (if applicable), some other programs that run in the background, then fire up a game like Half-Life 2, CS:S, CS:CZ or any other somewhat advanced game. Then come back and tell us how the performance in the game goes.
See, the more resources 1 thing uses, the more it absorbs from other programs, especially if it's higher priority. We don't know "what" your resources are (what a stupid accusation....it doesn't even make sense), but we do know what uses more resources than others.