Like GlenX said, Mandrake will format it for you. By default it will set up 3 partitions in that space - swap, /, and /home.
IIRC, the installer should come up with a partion scheme and format it for you (after you confirm). You *might* have to do a "custom" partitioning, though. If that is the case, try the following:
Swap should be double your RAM, up to a max of 1 Gig. More than that is waste.
/ should be 3 - 5 Gig for a normal install.
/home should get everything else.
Then mark all 3 partitions as needing to be formatted, and the installer will take care of it.