this link will explain how to install Ubuntu (.10. It is the same for 10.04
Look at the part for manual installation as that's how to create partitions. You
should do one for the / about 15 GB, swap 2xs memory and one for /home using the
rest of the available space. Backup your Windows drive before you begin, just in
case.

....softpedia.com/.../...-Ubuntu-9-10-126370.shtml