As long as it is a Basic partition (should be). You will wind up with a
boot options screen on startup that will let you pick which OS you want to
boot into. It is called 'multi-booting' and you should review this ng for
the many tips and explanations.
I managed it with the aid of a second 10 Gig drive I had left from an ols
system. Just set it to "Cable Select" and installed it next to my main HD.
Then connected to the internet on XP and opened up Vista in XP. When it asked
me which drive I wanted to install it on, just directed it to the one with
the cable select & let it run. Now when I start my system, it automatically
gives me the dual boot option.