Thanks BOAC,
I've been searching the internet and all I can find is how to make it happen rather than what the systems are capable of doing when the two systems are installed.
You are correct in saying that it is best to install the operating systems in chronological order. My question that stems from that is that both of my hard drives have an independant install already inplace. The XP drive is in my current machine and the Vista will come on the new drive. I'm guessing that I'll just need to do a "repair" of the Vista drive in order for it to find the other install.
I guess my next question is when I install a program does it write to an OS specific file or does it write to a common file that both OS's access? I'm beginning to wonder whether I should install all things in XP as Vista looks and recognises earlier windows installations but XP wouldn't have a clue as to what Vista is.
Still trying to figure out if it's worth the effort...I might run some trials over the weekend between each operting system to see if Vista is as bad as has been reported.