Boot Issues Linux on IBM Thinkcentre

I had installed Ubuntu 11.04 on my IBM Thinkcentre A51 having a physical memory of 256 MB.
It Ran Slow hence, I wished to uninstall it.
I did not find such an option however.
I later formatted the partition on which Ubuntu was installed, but i guess the default boot loader file also got deleted.
How do I make Windows XP as the default OS, Now that the PC wont boot.
