Install 2k first onto a different partition, XP will be unable to boot.
Then install 2k3 on another partition, that should restore XP to a functional state.
I don't know about exchange at all, if its a standalone OS, then install it before 2k3. If not, just set it up on the platform of your choice.
You will be given a boot menu at the end of it that will let you choose between XP, 2k server, and 2k3 server.
Good luck.