You should dual-boot. Install Windows XP first and then install Windows 8. This will cause the Windows boot loader to present a boot menu allowing you to start either Windows XP or 8. This strategy gives you maximum flexibility, as long as you are able to get XP drivers for all your hardware. But keep in mind that Windows XP will stop being patched in 2014 (I think in April 2014.)
And, just an FYI: Windows 8 lays waste to Windows 7 in performance, especially when transferring large multi-gigabyte files. File copies can also be paused! Other than better performance, it's very similar to Windows 7 and has the same compatibility options.
Just about the only thing not to like about Windows 8 is the lack of Start button, and that can be added back by buying Start8, an excellent $5 program.