|The only registry cleaner I'd recommend is CCleaner - it's free and it isn't too invasive in its default form. The other things it can do is to clean out un-needed files, that will always help, and also lets you disable, or remove, start-up items that may be causing problems, so it's a good tool to use as a starting point.|
Vista has a built in tool that can diagnose problems with start-ups, part of Event Viewer - rather than me trying to describe it, Ed Bott has a good article about it HERE
Having said all that, Vista isn't a great OS and often, as has been mentioned, a clean reinstall is the best option to get it running well again.
"I've always been mad, I know I've been mad, like the most of us..." Pink Floyd