Need help - Typing problems

Hi,
I was wondering if you could help me out a bit. I have had my mac a couple of years now and it has been performing great. Recently, i have been getting some wird typing issues however. They seem to come and go in no particular pattern. What happens is that while i type a word, sentance or the hole paragraph will be underlined and i will end up writting over it. Or the cursor is going to move to the middle of some random word or something like that. I am absoloutely sure that it is not caused by accidentally touching the trackpad. I can only assume that it is some form of virus but i have performed numerous scans and havent found anything. I was wondering if i could get some advise as to what i can do to get rid of this!!! It has happened more times than i can count while i am typing this! It is very irritating..
Thanks very much

Were there any liquids spilled on the keyboard in the past?

No, nothing like that!

Do you maybe have an external keyboard, mouse, or trackpad that is hooked into your Mac - maybe through a USB hub or bluetooth that you forgot about? If so, then maybe it is under a pile of papers or is experiencing a malfunction.

Can you plug in an external USB keyboard and try using that instead? If that works, then it would seem your internal keyboard is failing for whatever reason.

i have no external things at all!! I do not own an external keyboard to try as well, will see if any of my friends have a keyboard i can use.. i dont understand why, if the keyboard was failing, would it be so selective as to when to do it?

I would try using an external keyboard first, but if the problem still appears and you are willing to take some risk - try resetting the PRAM. Just search on this forum or google it to find out how and what, if any, the risks may be.