This is a Windows tip, not Outlook, but it’s asked often enough in Outlook forums that its worth putting in a tip.

The problem goes something like this: “I’m having problems opening attachments. They open with [some program I don’t like]. How do I make them open in a program I like?”

Locate a file of the affected type in your My Documents folder (save the attachment to My Documents if need be) then right click on the file and choose Open With... and select the program you prefer and click the box to always use the selected program to open the file type.