Here are the steps you need to take to safely uninstall Ubuntu from a dual-boot setup:
- Boot into your Live CD for Ubuntu
- Start a Terminal session with Ctrl+Alt+T
gksudo gparted and hit Enter
- Delete your Ubuntu partitions (you should have two, the main partition and swap). If you are unsure of which partition is your main Ubuntu partition, type
sudo df in a Terminal session and hit Enter. It will be the filesystem mounted on "/".
- Expand your Windows partition (it should now be the biggest partition) onto the free space by right clicking it and selecting Resize/Move
- Reboot into a Windows CD
- Choose Repair
- Choose Command Prompt
bootrec /fixmbr and hit Enter
bootrec /fiboot and hit Enter
- Reboot. Your computer should now boot into Windows XP.
If you want a full guide on how uninstall Ubuntu, see this website.