I use Microsoft Virtual Server to host my development environments.
These environments run in the background and I can use Remote Desktop
to access them in full screen mode. You can hardly tell you are in a
virtual environment.
One option you may want to consider is getting a low cost Dell desktop
and run MS Virtual Server on it and then use Remote Desktop from your
Mac to get into your development environment. You could get a Dell
system for about $400 which would be sufficient. Just get a large hard
drive (300gb+ and 16mb cache) and at least 2gb of memory.
To give each environment as much memory as possible I just run 1 at a
time and give it the memory the base install is not using. The great
thing about these virtual environments is that you can create a backup
of one of them once they freshly installed and revert back to the
backup whenever the VM starts to become unwieldly, like after trying a
few beta release packages.
That best part of this approach is that you do not fill up your hard
drive. I assume your Mac is a laptop. If that is the case you already
have limited space. You can easily get the 300gb drive for a desktop
for $100.
The dual boot option and the Parallels system are still possible, but I
think those are would be difficult to maintain.
I currently run a Dell Inspiron but hold my virtual machines on an
external drive enclosure which has one of those nice $100 hard drives
so I get the best performance out of my VMs without eating up all of my
internal hard drive space. And whenever I want to unplug and go I have
just 1 VM on the internal drive while my external has multiple
environments.
Brennan Stehling
http://brennan.offwhite.net/blog/