Tips on keeping a new XP install running smoothly

[bungadunga]

I have a tendency to fill my computer up with various crud, and after four years in which I couldn't be bothered to reinstall Windows I have ended up with a system in a sorry state. I gave up on my start menu once the Program Files menu cascaded past the edge of my screen and on to infinity.

My goals for the next install is to keep things more organized, but I wanted to know whether you guys have any suggestions on helpful programs. For example, it would be nice to have a database of what programs I have installed and what they've done to the registry, where the files are, etc.

Good programs for incremental backups (to DVD probably), programs that will defrag on a schedule, programs that will keep track of registry updates and let me roll back to previous setups, would all be helpful. Are there any good, free, and slim (in terms of resources) programs that will do this sort of thing? Do you have any strategies you follow manually to avoid crufting up your computer?