I just finished upgrading from Fusion 1.3.x to 2.0 which solved a different problem for me, however now I cannot get the VM to go into Unity mode. The "View" menu shows the "Current View" as being Single Window, and both that and the option for Unity are grayed out (see attached screen capture). The VM is running Windows XP Professional w/SP3 on a 24" Aluminum iMac.
Anyone have an idea as to why or how to fix?
The "Current View" being grayed out is normal - it's telling you what the current status is, not giving you an option.
Unity is dependent on (the right version of) Tools. Try uninstalling Tools, rebooting the guest once or twice (to let Windows redetect hardware if it wants to), and install Tools.