First the bad news. How can I put this... your app may not work on Windows Vista.
Which would be a shame. Microsofts biggest launch since Windows 95 - and your application won't even install - or if it does it won't actually run properly. Nobody wants this to happen. You don't want it to happen, we certainly don't want it to happen and your customers (new and old) absolutely do not want it to happen.
Why are we breaking your applications? Well - a number of subtle reasons combine but the biggy has to be... we want Windows Vista to be the most secure operating system we have ever released as the new connected world of people and software has made security THE number 1 reason... my mum won't let my dad renew his Broadband contract :-)
I did say there was good news. The good news is we are working on bringing together the right resources to help you make sure your application works great on Windows Vista. We have a new site focused just on this area. Take a look at http://devreadiness.org/default.aspx - we have whitepapers, powerpoints and great "cookbook" just for ISV. I will post again with the "best of" links - but for now - take out an hour or two to skim the site.