Once a year, backup all your documents and do a clean install of your operating system. Best way to keep the computer humming and registry clean. If you can't afford to do that, stick to google and sites like download.com for good suggestions on registry fixes.
There are some freeware programs that do just that - and are rated highly - I can't remember the name exactly, but it was registry something. Search google and the download.com site and make sure you look at the # of downloads and the rating and review of each.
