I too have a need to keep vista, as clients still use it and I need to work through issues - the ideal would be to run vista in a virtual machine - must get around to working on that one since I have now put windows 7 on the laptop too, (all legit full installs by the way).
Vista runs just fine in a VM. I keep all the recent OSes in VMs for when I need to support something that pops up, either on a business system, or a home system for family and friends.
As for compatibility and stability, Windows 7 isn't a new OS, like Vista was....meaning it wasn't built from the ground up. Windows 7, as some, including me, would argue, is more stable and compatible now than Vista has ever been. Waiting until a point when an OS is labeled as SP1 shows a lack of effort on an IT department's staff to properly use and test an OS before hand. So many said this about Vista...and as it turned out, Vista's SP1 was simply a security roll-up...make all those slow to the testing phase look sluggish and behind-on-the-times. Windows 7's SP1 will be the same.
Didn't that die with Vista ?
How to install a Vista upgrade on any PC • The Register
I am running Win7 Build 7600 in a vBox virtual partition right now - Vista is the host. This is working great. And I had to give it only 1GB (of my 4GB). Both Vista and Win 7 run without delay. What I like about it is that you can switch so easily between the two systems.
I suppose you could run it the other way around too (with Win7 as the host). I had written a little tutorial on how to install the virtual partition - in case you'd like to try it out: ( Tutorial: How to install Windows7 in a Virtual Partition « How-To Geek Forums ).
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