Forget about snake oil. Forget about registry cleaners. And quit using Isopropyl Alcohol to clean the case, because when you pass a cloth soaked in this stuff over your Windows COA sticker, it removes the key code.
If you want to do some cleaning..
.. go do dishes or take the vacuum cleaner out for a jaunt around your abode, but please please quit using registry cleaners.
The Windows NT operating system family (NT, Win2K, XP, Vista) is not phased by orphaned registry entries. They are ignored. There is no need to clean them out.
The Windows NT operating system family (NT, Win2K, XP, Vista) is a cousin to the old Windows 9x family, not brother, sister, mother, father.
The Windows NT operating system family (NT, Win2K, XP, Vista) is not prone to the constraints of its cousins.
The risks are simple enough to understand. You could lose part or all of your data, and Murphy's Law states that the part lost will be the most important.
If you can't resist temptation, don't install and run any cleaner utility which has an integrated registry cleaner. CCleaner is included in the above.
I'll wager that you do not have backups of anything, no restore CD/DVD, no clue how to restore from a recovery partition.
The last thing that you want to do is run a process whih is likely to destroy the only working computer presently in your possession.