1. Handle UAC on Vista ... Write Manifest File (by adding Manifest file using mt.exe)
2. Take care of Vista Virtualization(Registry & File Virtualization)
3. All executable files (including .exe, .dll, .ocx, .sys, .cpl, .drv, and .scr files) in an installation must be digitally signed.
4. Look at Legacy Windows Services codebase as hardening of windows services on Vista
5. Understand WOW64 Layer on 64bit Windows Vista OS.
6. Focus on File & Registry Redirection on 64bit Windows Vista(even on 64bit Windows XP)
7. Look at all your legacy Installshield/WindowsInstaller based Installers. They may stop working.
Links:
Windows Vista Application Development Requirements for User Account Control Compatibility -
http://msdn.microsoft.com/en-us/library/bb530410.aspx
Developing for Vista - http://www.regdeveloper.co.uk/2006/09/22/vista_for_developers
Create and Embed an Application Manifest (UAC) - http://msdn.microsoft.com/en-us/library/bb756929.aspx
Kate Blog - http://www.gregcons.com/KateBlog/CommentView.aspx?guid=682d4de9-572f-4a18-b822-19069e50410f