DUAL BOOT XP 32 bit and 7 64 Bit DO-ABLE??

So for dual boot .. install XP in one partition, 7 in another partition . Got it.
Now I have two qts:
1. How do you choose at startup XP or 7? (sorry for such a noob qt)
More importantly:
2. I want to install XP 32 bit in one partition, 7 64 bit in another partition. .. Can this be done?

I need the 32 bit for games and aps that do not run on 64 bit . I currently have two hard disks, one with XP 32 bit installed and the other with 7 64 bit installed. But it seems unless I swap out the OS hard drive that I don't want to start with, the PC starts with using the hard drive of the OS that was in use when the PC shut down, ... Confusingly express so just ignor this in favor of answering the above two qts, if you can .

Yes I just built a 64 bit machine:
EVGA x58 motherboard
Intel i7 920 CPU
Corsair 6 GB DDR3 RAM (3 sticks / 2GB)

Thanks for any/all advice!!!!! Reply direct to my email is fine with me as well.

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