Trutleoke,
I have not heard of a case where and older version of Hoster will not run on a vista computer. If you make all of the MTU suggested changes to vista, your older version may work but I've never done it so I can't be positive. (I use XP Home.)
If you have your older version of Hoster installed on one computer you should be ready to go (you are allowed to install Hoster on two computers). If you have your older version of Hoster installed on two computers you will have to submit a support ticket and let MTU know that you are moving one of your copies to a new computer.
4.08 is awesome. The new features are well worth the $$$. You should upgrade to 4.08 just to get these new features.
Your older version of Hoster will install in vista and you will be able to upgrade to 4.08.
I hope this helps.
Jim
