Since you are new to linux it would be best to read the installation README on the mandrake cd before you installed it. It seems that you allocated a big partition for mandrake.This is not a proble though. Mine is 2 gig for my home and 3 gig for all the rest plus 1gig swap file.
To learn how to get around linux may I suggest you get a Knoppix CD(www.knoppix.net
). It would familiarize you with almost everything in linux ,detects most of your hardware and perhaps when you have enough confidence then you can install it to you hard drive. Then you can try out other distros.