I have a win32 application which is working very well under XP. I am testing on a Vista box and unless i elevate the application to "Run as Administrator" it won't run.Also my app.won't run to fullest extent since my app.writes to specific system folders, access HKLM in registry etc. I am planning to change those pieces which are accessing system folders and registry inorder to work well with UAC in vista.
Do i need to do any specific thing to work on vista apart from above
I am not planning to recompile the code base on Vista or i won't be using any features specific to Vista. All i wanted is to say to my customer is that my app.works on Vista too :)

UAC Compliant application
Doffen
I have found the following resources to be the best starting points for developers:
Application Compatibility Cookbook: http://msdn.microsoft.com/library/default.asp url=/library/en-us/dnlong/html/AppComp.asp
Requirements for User Account Control Compatibility: http://www.microsoft.com/downloads/details.aspx FamilyID=ba73b169-a648-49af-bc5e-a2eebb74c16b
Going through a Vista certification process would also tell your customer that your application works on Vista, but that would definitely be overkill if you have just one customer who is looking for a verbal confirmation of compatibility.