64bit XP - Where?

I got about 4 Windows XP licenses. However, they are all 32bit. Is there a way for me to use one of them for a 64bit Windows XP, or will I have to buy yet another one?
Reason I am asking is because I want to install XP64 on our new computer (for programming, since it offers bigger limits!), but the system comes with Vista. What do I do?

:/ I guess I am SOL. I wanted to avoid dual booting if I could, but I guess that's unavoidable.
WinXP + Debian/Gentoo, here I come!