As far as I'm aware of, once CCleaner deletes files, they are gone in the same way as manually deleting these files and emptying the recycle bin. You could try using undeletion software (e.g. Recuva undelete freeware), which may be able to undelete some files, assuming you know which folders they were located in.
If you are trying to recover registry items, there are two ways you can do this:
- When CCleaner carried out the registry cleaning, it would have asked you to save a registry file. To restore this, go into the folder where you saved this file and double-click it. Then click 'Yes' to apply this to the registry. Now, all the registry cleaning CCleaner has carried out is undone.
- If you skipped that backup step or deleted the recovery registry file, you will need to carry out a system restore. Go into Start -> Programs -> Accessories -> System Tools -> System Restore. Now choose a date before you run CCleaner and perform the system restore.