You didn't say which OS you are using, but if it is Windows XP then the registry there is much more robust and forgiving that the registry from previous versions. Meaning it can take rogue and obsolete entries without any major loss in performance.
If your computer is running slow then you need to look elsewhere. Can you give us more details? Do you mean slow to start up and/or shutdown, or slow performance, slow internet?
Tell us more about your computer. The note in red font above each posting box tells you what we need to know. Also, what house-keeping do you do? What anti-malware protection do you use?