what is a good and free registry cleaner for vista?

Maybe someone could buy you a Windows 7 upgrade as a gift? That would be free to you... hehe

CCleaner is certainly a decent program, but I highly recommend Glary Utilities.

Also, I highly recommend that you make an image of your system drive in case the registry 'cleaning' doesn't go well. Personally, I only ever mess with the registry after I've made a backup image. Errors that registry cleaners make aren't always recoverable using their backups or even merging backed up entries into the registry manually and System Restore isn't always still functional in these situations.

Glary Utilities > http://www.glaryutilities.com/

CCleaner > http://www.ccleaner.com/

For making backup images:

Macrium Reflect > http://www.macrium.com/ReflectFree.asp

Edit:

Don't listen to Mark Brunson's spam... Advanced Registry Care is not free according to the site he posted, it is free to "scan" your computer, but it will of course cost you to have it do anything.

_

there are several software :

ccleaner - www.piriform.com/ccleaner

www.tweaknow.com

http://www.registry-clean.net/

CCLEANER by piriform