Ccleaner is a good safe tool.
The `WINDOWS/TEMP` files are exactly what they say, temporary files that Windows makes when carrying out functions. If Windows wants them in the future it will make them again.
Always backup your Registry before cleaning with any tool - even though Ccleaner will also do this for you. I have never had a problem with Ccleaner (and not heard of anyone who has) but it could happen. I use ERUNT click here to backup my Registry on a separate drive (I have two) but you can save on an external drive, CD or separate partition if you want. This would allow you to access the backup in an emergency. ERUNT makes backups that you only need to click on to get them to reinstall.