Rather than changing your NTFS partition to FAT32,
just download a
KNOPPIX Linux Live CD and use
QTParted to resize your drive and create the free
space you'll need for Linux. Then when you install
the new Linux OS to the free space you created, you
can format it with the tools available in Linux.
I've done this several times to laptops, but rather than
install Mandrake, I've installed Slackware. When you
are in the installation of Slackware you can format the
partition easily.