You didn't mention what version of windows you are using, so I'll start with the basics.
Go to FIND/SEARCH and type in *.chk and any files that begin with File000 and increase numerically can all be deleted (right click and delete right from the search window). These are Scandisk files that are garbage left over after scandisk fixed errors.
Now do a Search for *.dbx and look at the size of the SENT ITEMS and DELETED ITEMS files. These are copies of every email you've ever sent or deleted in Outlook Express. If you have any that you really need to save, open OE, create a NEW folder and locate the emails you want to save and drag them to that folder. Now go back to FIND/SEARCH and look for *.dbx again, and right click and delete those two files. They can get pretty huge after a while.
There are settings in Scandisk and in Outlook Express that you can change to stop these files from existing at all, but if you change the setting in OE, make sure that if you have emails you want to keep, save them FIRST (if you are sending mail that you need a copy of, email it back to yourself with a BCC email and then save that copy).
There are many other things you can do to regain space, so once you let us know what version windows you have, we'll give you a few more tips.
which files and or folders can i safely delete to clear up space? I have lots of cabinet and wink.