How to make Windows bootloader the default?

When I got a new computer, I installed Ubuntu and Windows XP on it. When I turn it on, GRUB shows up and lets me choose between the OSes. All right so far.

A while later, I decided I don't want Ubuntu anymore (Linux fanboys, refrain). I deleted its partition, but I realized too late that GRUB depended on it, so the computer wouldn't boot. I installed Ubuntu again and it's working fine. So how do I tell the computer that I want it to boot directly into Windows?

Use EasyBCD to take Ubuntu from your bootloader

EasyBCD will overwrite GRUB, after that format the Ubuntu partition: Done!

Edit: works in XP, yes

You need to reinstall the Windows NT Loader (yeah, its NT even for XP) to the primary boot partition. Thankfully, doing so is incredibly easy.

1. Boot in Recovery mode from an XP CD. You need to boot from the CD to do this.
2. Run fixboot
3. Run fixmbr
4. Reboot

As GeneQ added in the comments below, if fixboot and fixmbr fail, you can always use fdisk /mbr. The fdisk method will work on older computers that have MSDOS/9x bootdisks.

When else fails (otherwise use the fixboot/fixmbr method instead) and need to get back to your Windows XP bootloader instead of the one installed by your Linux distro, simply follow these instructions:

1. Boot up with your Windows XP disc.
2. Select the option Recovery Console.
3. At the prompt, type: fdisk /mbr
4. Restart your computer.