Save the file to a folder. Go to that folder and select the file. Shift-right click. Chose Open with ...
Select your favorite program to view tiff-files with and take care to check "always use this program to open files of this types". This need only done once, and then you will be able to open the attachement itself, I think.

Programs to try:
- Internet Explorer
- Irfanview (download from www.irfanview.com)
- Quicktime
- Microsoft Photoeditor
- Adobe Photoshop
- Quickview

Hope this helps. If not, post again with details about what goes wrong.

Kees