WIN-XP - TOTAL File/Memory usage where?

I'm having a senility moment, and can't find *where* I can see how much
of my hard drive I am presently using. Under view I set it to show file
size, but it won't show except in an individual pop up. I thought
somewhere I could also see total file size in the tool bar, but it's
been so long since I looked for it, I've forgotten where.

When you look at the C drive... the available figure... is that what's
available after all the Windows programs reserve space or is that
really what's available after everything that is on the computer now?
My question is because there is so little space used on my laptop.
TIA... to anyone who can break through my mental fog. :)
bj