I think your 8m free is your hard drives cache.

I run 80 Gb drive with Debian and Win XP
have 160GB drive with knoppix and storage partition.

I set up all my partitions first then installed XP then installed debian and knoppix.

Telling XP to only use one particular partition. I then specified which partition debian and knoppix was to use.

My partions are Primary HD
20GB windows XP /dev/hda2
58GB Debian /dev /hda1
2GB Swap /dev/hda3

Secondary HD

10 GB /dev/hdb1
2GB /dev/hdb2
148GB /devhdb3

To setup partitions I boot with knoppix and used Qparted to partition.
I did start with empty hard drives.

hope this helps