I have a very small drive C:, only 20 GB and used only 10 GB (XP64). I don't install anything in C. Some nasty programs don't give any choice than to install in C, I try to avoid using these programs and even if installed I try to move them to other drive once installed.

I have a drive D for only the swap file (virtual memory) and a temp folder, nothing more there and have no swap in any other drive including C.

The advantage of a small drive C is that for Microsoft only exist drive C, all the mess is done there and the other drives are always clean of Microsoft's garbage. As C has limited capacity the trash cannot grow forever there, in one moment there will be no more room for trash and so, a forced cleaning operation.

The other big advantage of a small C is that I can create a disk image that fits inside a DVD, it gives more or less 3 GB compressed, in my case. If some program or crapy driver update makes my computer don't work anymore, I restore drive C from the image with a boot CD and in less of 5 minutes I have my Windows working again. I never re-install Windows !!!

All my programs and data are in E,F,G,H,I,J,K and L   M is the DVD

Stupidity also evolves!