You're lucky. Just a few days ago I went through the same problem and was glad to have the email address for Peter Kazanjy, the product marketing director for VMWare Fusion, in my address book because I emailed him directly to ask what was going on.

The bug that you and I have both encountered is unique to the Macbook Air and is one that I'm sure will be fixed in the next update from VMWare, somehow: if the program looks for a CD/DVD drive and there is none (which is the case uniquely on the Macbook Air) then it crashes.

The solution is quite literally to hook up a CD/DVD drive, but that's not really a long-term solution because I know that when I want to run Vista, I don't want to worry about my external drive! Fortunately, you can make one tweak to the configuration of your virtual OS and solve the problem forever.

But it's not quite that easy either.

What you need to do is uncheck "Connected" on the Settings window, but if you just click on "Settings" within your VM, you'll find that it's grayed out:

How do you get it so you can unselect it? Easy, you need to hook up an external drive.

Do that, quit VMWare Fusion, start it up again, and now you will find that the very same config window lets you uncheck "Connected" and change the settings appropriately:

Make that change, save your changes, and you should be able to disconnect the external drive and never worry about it again.

Clunky, but think of this as a workaround more than a solution. The solution is, I'm sure, forthcoming from VMware in the guise of a simple patch.

By the way, Peter explained to me how they've managed to reproduce the problem without having a Macbook Air in the office: "We were able to reproduce in house by opening up a Mac Pro and attaching and detaching the cables to the back of the DVD drives in the casing. Sure enough, it shows up there too." Good solution, and you can bet a patch will be out quite soon!