Is premiere pro 1.5 compatible with Windows Vista?

NO, it is not compatible. On most systems it will hang. It will install and activate, but you won't be able to get it running enough to deactivate it so you can load the software on another computer. If it hangs you can remove 3 Plug ins from the Premeire plug ins folder that seem to make it freeze. These plug ins are GPUPageCurl.AEX, GPURefract.AEX and GPURipple.AEX this should keep it from freezing on open. However there are still other problems that arise such as Audio sync problems and more.