Clean Up Unused Files
Many programmes leave files behind on your hard disc that are never used again. These just take up disc space and they can slow down your PC.
Windows includes a utility that does some of this work for you. Open Windows Explorer and select your hard drive, right click on the hard drive and select properties, then click on the Disk Properties button. This brings up a dialog box where you can select what areas to clean up, and how much space this will make.
Temp directory
This is where programmes are supposed to leave temporary files. The directory varies depending on your OS, and might be c:\temp or c:\windows\temp or even c:\Documents and Settings\username\Local Settings\Temp. Any files left in here should be able to be deleted without affecting anything else. Delete files with names like ~*.tmp or *.tmp. Don't delete anything with today's date - it might be still in use.
Browser temporary files
Your web browser (Firefox, Opera, Internet Explorer) stores copies of all the pages you browse, to speed up surfing. In the preferences or options menu, there should be a place to clear this cache and to set it's maximum size.
Checkdisk Files
The scandisk programme puts file fragments that it finds in the root directory, with names like *.chk. You may be able to recover content out of these files, or just delete them.
Deleted Email
Emails that you delete in your email client (Thunderbird, Outlook Express) go to a folder with a name like Trash, Wastebin or Deleted Items. Clear this out every week or so. Better still, set it to clean out the deleted items every time you exit. In the preferences or options menu, ensure the "Empty messages from the Deleted Items folder on exit" item is checked.
Other Unused Files
There can be lots of other files sitting around in the backwaters of your hard disc. Files like old word processor documents, spreadsheets, saved games, downloads, etc. Search these out and delete the ones you no longer need.
Recycle Bin
Files you delete go to the Recycle Bin. This is handly because you get a chance to recover accidental deletions. However, the Recycle Bin still takes up disc space, so it is a good idea to empty it every few days. Double click on the Recycle Bin icon, and go to File / Empty Recycle Bin.