Powerpoint will run on either VISTA or Win7 the only difference might be the version of powerpoint that you are using ie. if you upgraded to a new Powerpoint version along with the OS change in which case you should save it in the older powerpoint format under the save as options:
For example in the 2007 version the save as options include saving in the older 97 - 2003 format. Or you could convert it to say a .pdf format.