I have Vista with multiple users. In my sons section, he has changed a setting that is causing Adobe Reader to attempt to open various file types including Internet Explorer. Getting an error that the file can't be opened. NO DA!!! In all the other sections, this problem is not occurring. Currently, I must download Reader everytime I want to read a PDF file and then delete so my son doesn't have issues in his section. The Adobe Reader icon is even showing up on the Desktop replacing the other files icons.