Does anyone else's computer do this annoying thing?

I’ve been having trouble typing lately. Basically, the cursor just does whatever it wants. It will move mid-typing so I end up typing in the middle of words I had previously typed, or it highlights chunks of text so when I keep typing it deletes what I had before.

It’s super annoying, has anyone seen this before or have any ideas for a solution?

I have a Mac 10.4 that’s about three years old. It’s otherwise in fine condition. One thing is that the left side of the clicker seems to be depressed compared to the right side.

Thanks!