Danny that is the way I went about it and I highly recommend it. Especially for those who are running a business and are concerned about making big changes like that.
When I went from my XP 32 bit install to my current Win 7 64 bit install I bought a new machine and just spent the time setting it up completely on the side. Did not touch the then current XP install at all. Just left it alone and fully operational.
On the side I set up the new machine installed the OS even bought a new RME audio interface for it and a new midi interface. Tested it fully and got it all running up sweet. Then when things were a little quieter for me I just installed it into my main setup.
I actually did not fully remove the XP setup either but rather moved it to the left and connected it up via audio and midi and networked the two. The two computers running at the same time is rather excellent. I can harness the power of the old setup anytime. It also allows you to run older programs, VST's etc...
BTW the new Presonus 192 interface is very nice. I have heard it. As is the CS18Ai as well and they both integrate pretty tight with Studio One 3 but that is a different story I guess.