I'd recommend Linux.
OK, seriously, beware of some of the registry cleaners. I used RegCure on my XP machine and it managed to delete some installer entries necessary for MS Office updates. To be fair, it was my fault in as much as I let it delete these entries which it had flagged as redundant, but how are you supposed to know if they are really needed? Since then I've become very suspicious of this type of application, although CCleaner seems OK.
For backups on XP I use
ViceVersa which does the job of synchronising files between drives/partitions very well. For disk imaging,
Acronis True Image seems to work, and I've also used it to clone an XP drive onto a larger drive.