You really need to give more information. What's your primary OS? Are you doing clean installs of all of them? What do you want as a bootloader?
The set up is much easier for Vista than for XP. You can use EasyBCD to set up booting of all 3 from the Vista bootloader.
As Juggernaut stated, using GRUB is a good choice. You will have to manually add the OSX install, but if you install Linux after Windows then it should autodetect Windows.
In GRUB, for OSX, you can use chain0 file from the OSX dvd. Then add this to the GRUB config file:
title OSX86
chainloader /etc/chain0
Or you can use GRUB directly and add this:
title OSX86
root (hd0,0)
chainloader +1
With the hd0 indicating the drive and the 0 indicating the partition. You'll probably need to change this.