What are the full details on making a partition on a hdd?

im running an XP media center PC and ive been trying to look everywhere for details on how to do this, even yahoo answers and nothing helps me. ive fallowed other directions on how to make a partition by going to computer management, but when i right click on the hdd i want to partition, it doesn't show "partition" or anything, it just shows "open" "explore" "change drive letter and paths" "properties" and "help" even after i just format the one hdd i want to partition. please help me if you can?