Keep your hard drive clean with Lifehacker's Windows Janitor script
This could be your web browser's default download directory, which fills up with e-mail attachments, installer files, music, and videos. But whatever directory it is, odds are it's taking up more hard drive space than it should.
Windows Janitor lets you monitor a folder and regularly delete any file that hasn't been updated for more than 30 days. In principle, this should automatically clean up all the files you don't really need. But proceed with caution, because some files you download may think they haven't been modified in 30 days or more when you first get them. In other words, do not set Windows Janitor to monitor a folder if you've got files you can't afford to lose in it.
Of course, there are plenty of other ways to keep downloaded files from cluttering your hard drive. For example, you could set your desktop as your default download directory. You'll regularly be confronted with every file you've downloaded, which should serve as reminder to either file away or delete each downloaded file when you're done using it.