When trying to install my free copy of windows 7. It comes up with an error message before i even get started. It says, This installation disc isnt compatible with your version of windows. To upgrade, you need the correct installation disc. But I went through dell to do this and shouldn't have the wrong disc. I have windows vista home premium. The disc says win vista HmPrm - Win 7 HmPrm. Which is the right upgrade? Please help!!