Drugged dwarf, unfortunately when you reformat you will lose all data currently on your computer. What you should do is over the next few days start backing up what you need. I'd advise using DVDs as they hold so much more than anything else. You will not be able to save your installed programmes so don't even both trying to save your Pinball high scores. Instead try to build up list of programmes installed so you can quickly find them again.
There is a free program used by Linux (during the installation process) that will repartition your hard drive in a non-destructive way. You defrag your C: drive, then boot Linux from a CD and repartition the drive, making C: a little smaller and creating a new D: drive.
When you reboot into Windows, the drive will be there without a filesystem on it, so you'll need to format it. Now you can copy your files from C: to D: (basically My Documents and similar various folders). Unfortunately, many programs still store data
under Program Files (idiots!) so you can't be sure you've got everything unless you go through every folder. (sigh)
If you run out of space on D:, do the above procedure again: defrag C:, extend D: a little bit, then reboot Windows and move more files.
I'm not sure what the name of the tool is, though. Does anyone else know the name? I know there's parted
and the graphical qtparted
, but I'm not sure either are used by the installation program. (And yes, the install process uses a different one, I think.) Of course, you might not need the name at all, since you can just boot a live Linux CD (such as Ubuntu) which will already have the program on it. The problem with those live CDs is that they don't typically commit the partition change until they begin the installation, so you'd have to actually start the Linux install. When the installation is done, boot into Windows and reformat the partition that was just installed to! But this process will only work once -- you can't go back and resize the partition to make it bigger after moving some of the files, because they'll be overwritten during the second installation.
Anyway, as I said earlier. Good luck.