To be compliant with MS requirements for certification, the bit you see installing to the all users folder as far as I've found, can't be moved or changed.
The program can, as you have found.
IMO, that space is way too small for Windows alone.
I'd get partition magic and repartition that drive. Can you move or uninstall other things that reside on C? or D?
the OS won't be stable as it is anyway. It's hard to believe you don't have other issues............
I refuse to run windows with less than 15% free space on the OS drive, and never under 1.5gig
When i see those numbers, I cringe and work to get it changed.
I guess it's possible I'm wrong, but I doubt you'll get the defs and all users folders to move.
How do you get windows to update security and other updates with such a small free space? does it run updates?