im with cook on this one as well.
Ccleaner is strong but not so strong where it will delete important reg files you need and even if that were the case,Ccleaner has a back up reg cleaner option so if you do delete something that is needed you can revert it back to normal using the back up.
i will suggest one thing right now though.
PLEASE , Heed my warning,DO NOT DELETE anything in the registry unless you know exactly what you are doing.
it one of the most sensitive parts of your computer where if you delete something you could possibly leave your computer in an un-operetive state.
in simpler terms,messing with the registry can leave your computer useless.
turn it into an over sized paper weight.
i would use Ccleaner like mr cook says.
it does the job very well and its a free download
have you heard of it?
download it here:
http://www.piriform.com/ccleaner/download/standard its a free download