I have found that,if you can afford this option,its the best way to go:
Get a decent removable hdd rack with an extra tray and put your operating systems on thier own hdd.You can use smaller sized hdds and its as simple as pulling one tray out and putting another in.
My setup is like this:
2 computers with 4 operating systems Win2k,winnt wkstn,winnt server,Mandrake 7.1.Each on it's own hdd.
I use the windows OSes for a home networking lab to help me with my education and Linux for everything else.
Like I said,this is my solution to all the problems that arise when using more than 1 OS.