It doesn't make a whole lot of sense that the primary partition gets full when you do nothing with it. I'd say the ISP tried to install some crap on it (like windows updates) or it's been infected.
It's possible to make the primary partition larger with partition magic. I don't know if that's possible through a remote desktop, and I wouldn't do it without making a backup.
Now, I'd take this opportunity to wish you all a merry christmas. A bit belated, but it's the thought that counts. Heh.