Can you tell us how big the hard drive is and how much free space there is? One of the easiest way to free up space is to go into Control Panel > Add/Remove programs and delete any programs that you no longer use. To do a cleanup of temp files download and run with the default settings CCleaner - Home (do not use the included registry cleaner, or for that matter any registry cleaner .. we've found that they can cause more trouble than they're worth).
What data files can be saved to CD instead of remaining on the HD?
Here's enough to get you started, after you've done the above steps, reboot your PC and let us know how much free space you have now. Keep us posted.