If you’ve installed Ubuntu as a dual boot with Windows then removing it isn’t easy (which is a shame that they make installation so easy but make no effort in assisting with uninstalling).
Removing the partition that Ubuntu lives on is the easy bit – sadly, it also removes GRUB, which is the menu that allows you to choose your OS during boot. As a result, you’ll simply get an error during the next reload and you won’t be able to even start Windows. Nice.
It would appear that you have to repair the Windows MBR (Master Boot Record) – this will restore the standard boot method. I found an excellent article on how to do it but, sadly, as this was on a Netbook (and is often the case with Laptops these days as well) I didn’t have any Windows installation disks.
However, after doing this and following the instructions in the first article, I found it booted just the same (at this point I hadn’t removed the Ubuntu partition, as I still wanted to be able to access Windows!). In the end, I came across a utility named MBRFix – this can be run from Windows and is a command mode utility to perform various actions on the MBR, including restoring it.
Install MBRFix and run the following command (assuming you’re running XP)…
MbrFix /drive 0 fixmbr
Then simply reboot to ensure it’s worked – the GRUB menu shouldn’t appear and XP should boot as normal. Once this is confirmed, remove the Ubuntu partition and then use a free partitioning tool to reclaim the space.