Just an idea that you may not at all be interested in...you said you are only using 10GB for Mandrake and want more. Since the rest of your hard drive is being occupied by Windows, you could mount your other partition at boot with full read-write access and save/open files from that partition, making good use of the space. The only files that would be on the 10GB Mandrake partition would be those particularly related to that OS, and that space should be more than adequate. If you are interested in this, try adding this line to your etc/fstab file.
/dev/hda1 /mnt/windows vfat uid=500,gid=500,umask=000,exec,dev,suid,rw 0 0
Sorry that I can't help with the use of partition programs.