ftl,
For what it's worth, X3 will run on Vista. The documents indicate this, but it is not supported by Cakewalk.
I have been running it on Vista Home Premium(32 bit) for several months. The only significant glitch so far has been the VST scanner and related Plug-in Manager.
The VST scanner included with X3 calls a port that does not exist in Vista. It's an easy workaround, if you know it's coming, though.
Before you install X3, rename the VST scanner and plug-in manager. Add a bogus word to the end of the filename.
The X3 install will add a new VST scanner and Plug-in manager. Delete these. Then remove the bogus word from the old filename. If you have any VST's in other folders (ie;Steinberg) you will want to move them to Cakewalk/VSTPlugins. From here, when you open X3, it will scan this folder, and you should be good to go.
Of course, if you have upgraded to W7/W8, it's a non-issue.