Basic advice for cleaning registry on XP?

So my second computer is about 5 years old, and it's starting to be slowed noticeably by "Windows rot." A lot of it probably has to do with leftover garbage in the registry from the dozens and dozens of programs that have been installed and uninstalled over the life of that machine, but I am really not well versed on how to clean up the registry.

I know re-installing Windows would probably solve most of those problems easily, but I don't want to do that because I've got so much stuff I don't want to lose. I also don't want to just go in there and start messing with the registry, or download a program that I'm less than sure about to do it for me, because I know that can really mess things up if you do it wrong. Basically, I'm just looking for any recommendations from someone who has successfully done this before.

I've never used that ^ program. I personally use ccleaner.

have you tried reducing to an absolute minimum the number of applications that start up when windows start up? Slow start ups can be the result of too much crap running in the background that start up as windows starts up. My networked pc at work has so much crap running in the background that it takes nearly 10 minutes to fully boot up in the mornings.

You can see and reduce the number of applications that start up when windows starts up by clicking on 'start' then 'run' then typing in 'msconfig'. However this is fairly common knowledge now so I would be surprised if you did not already know this.