What is the purpose of normal.dot?

I've noticed that my computer sometimes slows down to a crawl for about 5 minutes while running various programs...then it goes back to normal for awhile (like a half hour), then it slows down again for five minutes. Very annoying.

It also takes a VERY long time to complete its startup...like 4 or 5 minutes. I've never seen any other machine take so long to do that.

- LH