I have a system restore on my computer and have had to use it once for another problem and that fixed the problem. Will restoring fix registry errors as well or am asking for more problems?

My PC slow down, I've scanned it several times with different antiviruses – nothing. So I think thats all because of registry errors.

I have had my computer for about 3 years and it is becoming slow because of registry errors and things of that nature. Does anyone have a good suggestion for a program that can help and clean up computer? I have a dell and I on XP. Thanks in advance.