If you get a chance to toss some more RAM into your specs., that will give you an immediate boost, and most efficiently help out some of your lag. KL has some good points filters that may fight your SH3, and ATI cards are known for more fuss than others. Hang in there, you have the best bunch of guys and gals here to offer their help.
By the way; a1, that seems to be your first post!
Welcome aboard.