ubun2^beta

I want to uninstall Ubuntu and repair the MBR so it boots to Win XP normally. How do I do this?

I had windows vista and ubuntu 9.04 on my machine. Ubuntu has installed grub boot menu and it automatically detected windows vista installation and added it to the grub boot menu.
 
Now i installed windows seven and looks like it screwed up the grub boot loader. When i boot all i see in Windows Seven and Windows Vista from the boot menu (this is not grub boot menu). It is the windows boot menu. Now I can't even access or boot to my ubuntu.
 
How to fix this so that i can get my ubuntu back?

When i installed ubuntu on my windows vista machine, i had two menuitems for ubuntu and two menuitems for windows vista in the grub boot menu. I edited the boot menu list file and set vista as my default boot operating system. So, if i don't hit enter, it by defaults boots into windows.

I recently installed ubuntu on my laptop which already has windows xp on it. Ubuntu got installed successfully and shows the Grub boot loader.
 
Since ubuntu was the latest installed operating system, it always defaults to ubuntu. Since my job requires quite few microsoft products like office, etc., i need to choose the Windows XP operating system in the menu item and it boots correctly. It will be very helpful to change the default boot loader to windows itself so that i don't need to choose it every time. Please suggest, thanks.