Partitioning my Harddrive

I have downloaded Mandrake Linux and I am going to burn it onto a CD soon. I hear it is good to partition your harddrive when you add another operating system. I have a C and D drive. The C drive contains the majority of the memory will the D drive only contains about 2GB. I am wondering if I can just install Mandrake onto the D drive? Can I make the capacity of the D drive larger? Am I going to have to make a whole new partition? Someone please help me out. Thanks.

Oh yeah...if I do have to make a whole new partition, how do I do it?