That is definitely not normal, but it's very difficult to say what the problem might be without more information. Open Activity Monitor and look at the System Memory tab. Compare page outs to page ins. If page outs are more than 10% of the page ins, you're having memory problems and need more RAM.
How much hard drive space do you have free? If you don't have about 10% of your drive free, you can start having all kinds of strange problems.
Try starting up in safe mode... do the problems happen in that mode?