The certificate you use to sign your ClickOnce deployment will expire at some point. In the past, creating or purchasing a new certificate and deploying an update to your application always required the customers to uninstall and reinstall the application. This is no longer always the case. This GoldMail summarizes this issue, and provides solutions if it is a problem for you.
This download contains the written article with details and sample code (VS2008, C#). If you are a VB developer and can’t figure out how to translate this to VB, post a query and I’ll see what I can do for you.
[edit 7/7/2011 Move zip file to Azure blob storage]