[Fish]

Yeah, don't bother with registry cleaners. They don't work and it's much more likely it will cause further problems.

Don't bother with defrag, unless you're still running WinXP. It's not necessary and even in older OSes, it wasn't the magic cure all that it was touted as.

In addition to using msconfig, another more advanced method is using the Services app. Go to the Run command and type services.msc. There you can manage every single service running on the machine. You can change the behavior from Automatic startup to manual, and a bunch of other neat options. Don't turn things off that you don't know though. If in doubt, look up the service online to see what it is and what it does.

Also, as phisherman said, you might consider a rebuild. It's not that difficult and you'd be amazed at how much better the machine would run afterward. Once you do that once, you'll start to understand how to manage the OS to make a rebuild relatively painless.