With very few exceptions, if you design a Windows program correctly it should continue to run on new versions of Windows ad infinitum. But Microsoft also adds new features with new major versions and you may want to incorporate them. Alun Jones, a Microsoft Security MVP, author of the Tales from the Crypto blog, looks at this issue with respect to a program he writes and sells, the WFTPD FTP server. He's decided to "Vistafy" it. Interestingly, none of the changes he proposes (as far as I can tell) would break the applications on other current versions of Windows. He's mostly talking about changes, like moving away from CPL files for the Control Panel, that make a program work better in Vista, and that conform to best practices. It's all worth considering for your own apps.