If you have a pc which is already slow, then one of the last things you want to do is install more programs to run in the background while your pc is on.
I would recommend CCleaner which is at the top of the list on DaveR's posted link.
I have used it for a number of years for a final clean up on pcs after virus removal.
It is an on demand program, so only runs when you start it up.
It cleans all the temp files etc from your pc.
It has a registry cleaner, which I have never known to find/delete any 'needed' entries, it also has a startup section to manually stop un-needed programs from running on startup.
It can also perform a few more tasks if needed.
The best bit is - - it's free!!!!
More info here:
http://www.piriform.com/ccleanerDownload from here:
http://www.piriform.com/ccleaner/download/standard