Neither relate to free space on the drive..
Double click 'My Computer'.. right click C drive and select 'properties'..
you should now be able to see space used and space free..
You will get warnings about 'virtual memory' when the free space on the hard
drive falls below the level able to support the pagefile set by the user or
system.. while it is possible to set a pagefile that will (for now) stop the
warning, eventually, it will reappear..
You do have options..
One of them is to burn music, pics, documents to CD (you should do this
anyway as a backup insurance should the hard drive fail), and then delete
the files off of the hard drive to regain space..
OR..
Install a larger hard drive.. this could be an internal type or USB external
drive.. either could then be used purely for storage..
OR.. as above but clone your present installation to the larger drive, and
then use the old one for extra storage..
In the event that you opt for a larger drive, please note that you should
still back up to a media type that can be removed and stored in a safe
place.. CDs and DVDs are very good for this..