Hah, you could be a brave soldier and boot into safemode, (tap F5 F5 F5 and stop when you see the Windows logo)
Once in safe mode, it's all big and ugly... click Start, Run, type msconfig, click ok.
Click the startup tab and uncheck anything that is considered junk to you. If you don't know what an item is, Google it. After that is done, restart in normal mode and install CCleaner.
http://www.ccleaner.com/
In CCleaner's tools menu, choose Uninstall and start removing junk applications. Get rid of all of what you consider junk, and Google items when you don't know what they are. Restart when needed, and after you are finished, use CCleaner's registry cleaner tool.
THEN, do a CCleaner cleanup. This should speed things up and free up some space.
Please note that MSCONFIG is not available on Windows 95 or earlier versions. I think it first appeared in Windows 98. Good luck!