If you upgraded from a previous version of Windows or gave up your dual-boot system to stick with Windows 7, you might be scratching your head wondering how to remove them from the boot menu. Here's how to do it.
Over at the How-To Geek site (my home away from Lifehacker), writer Trevor covers the process of getting rid of the old entries, which is an easy task from the command line — first, open up a command prompt in administrator mode by right-clicking on the entry in the start menu. Then just run the bcdedit command to see a list of all the entries, copy the unique identifier to the clipboard, and then paste it into the command like so, replacing IDENTIFIER with the actual code from the clipboard.
bcdedit /delete IDENTIFIER
It's an easy process once you go through it, but keep in mind messing with the bootloader can be dangerous, so proceed with caution. This tip should work for Windows 7 or Vista, but if you haven't upgraded yet, you can still clean up your Windows XP boot menu easily. Hit the link for the full step-by-step walk-through if you aren't well-versed in the command-line.
Remove Ubuntu or XP from the Windows 7 Boot Menu [How-To Geek]