Mandrake's installer includes a partitioning tool. During the installation process, you you will come accross a menu that gives you several installation options including reformating the hard drive and installing Mandrake. Select custom partioning. You will then be taken to a nice GUI partioning tool that shows you what partitions you have on your hard drive. You can resize, delete, and create partitons here.
If after you have had time to fully evaluate Mandrake, you find you really do like it a lot, I urge you to support Mandrake by either purchasing a boxed copy from them or send them a payment to join Mandrake Club. The membership fee also goes towards the cost of mantaining the Mandrake project.
Mandrake's site should have plenty of documentation that you can refer to for help http://www.mandrake.com/
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