When I was dual-booting XP and 7, I used GParted Live (
http://gparted.sourceforge.net/livecd.php) to shrink my XP partition by about 40 GB, giving that to a new partition that I installed 7 onto.
As I recall, 7 simply installed the boot manager that Vista and 7 use all on its own. I didn't need a third-party boot manager.
If you do plan on using GParted, PLEASE make sure to back up anything important before resizing your active partition(s). While I've never run into any difficulties, they are, certainly, possible. It's always best to be prepared.