I want to partiton my hard drive so I can dualboot Windows 7. I already installed Ubuntu as my only OS. I tried GParted from the software center but I can't unmount the main Ubuntu partition. Help please?
If you want to resize your Ubuntu partition with GParted, you cannot run GParted from the installed Ubuntu system.
Therefore, you should use a live Ubuntu CD or USB key to boot into it and then resize your partition and make a new one for windows. Theres is a guide here: Resizing my linux partition
You will probably have to use the live Ubuntu to fix the bootloader after installing Windows: Recovering Ubuntu After Installing Windows