open windows explorer Flag-E keys
right click on the C drive and do properties, run disk clean up, may take a while, when it is done calculating, select the "more options" tab and then system resore cleanup, when done with this do not close it, select the disk cleanup tab and unselect the compress old files if it is checked and check the boxes of things you wish to clean out then hit OK and it will finish clean up for you and then close it. Do a properties again and see if you recovered enough space for your needs..
I think I really do need to reformat, but I'm a little reluctant (nervous) about doing so. It will be the first time I've tried, and with my luck this pc will probably end up on a shelf in the basement until I have the time to try to fix whatever I tried to fix. Where to go to get instructions?
Denny D, did Dell put you on their payroll yet? Do you get some kind of "preferred guru" discount for all the problems you've solved for everyone??
What is your primary motivation -- responsiveness? (speed)
If it were mine, before I do anything with the hard drive like format and re-install, I would make sure all critical Windows updates are current (may require re-boot two or more times during the process -- some have dependencies) and also run DEFRAG once a week. In old, old systems it was not a huge problem to let defrag go by for a year or two but NTFS (as I understand) benefits from much more frequent executions of defrag. ("My Computer" RIGHT-click "Manage" and click Defrag)