Firstly, my apologies that you've had to move to Vista.....I hope Microsoft's latest and greatest OS proves more successful for you than it did for me (and everyone I know)!
You're ActiveSync disc won't install because ActiveSync doesn't run on Windows Vista - you now have the privilage of using Windows Mobile Device Center. Details and a download link are here:
http://www.microsoft.com/windowsmobi...icecenter.mspx
It's backwards compatible with Windows Mobile 5 (which is what will be running on you XDA Mini) so you have no concerns there.