I have a dual boot machine with XP Home and Mandriva Spring 07. I had no problems dual booting from my machine with XP installed.
Prior to this however, the laptop had Vista installed and i tried to dual boot it with Xandros. Xandros installed fine and ran perfectly but when i tried to boot up vista it would hang at startup. I remember reading somewhere that Vista didn't like dual booting with Linux without a fair bit of tinkering. This could have been remedied in Mandriva 08 though.
There is an article on it
here with a link to a guide.