Hi smurfchops,
I think if you right click on the attachment and select properties you will see the file extension. For example, a Word Document will end in .doc, and Excel file will end in .xls, a text file will end in .txt.
If you can find out the file extension, then it should be easy to find out what software you need to open it.
Alternatively, when you get the message stating that windows cannot open the file, select the web service option and it should help you find out what is required.