I have done this before.. and iirc all i done was format the XP partition, then I ran bootrec just to be sure:
1. Put the Windows Vista installation disc in the disc drive, and then start the computer.
2. Press a key when you are prompted.
3. Select a language, a time, a currency, a keyboard or an input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type Bootrec.exe /rebuildBcd, and then press ENTER.
Although someone is now going to tell me there is an easier way
