Older than I remember, and i don't have it installed so.. lets see.
If you open the message, check the file menu. It might only allow you to
save the attachment from there, so... If there isn't anything there to allow
you to open the attachment, close and reopen and hit tab til you hit the
attachments. You should be able to arrow key through the attachments and
hit enter or use the context menu button key on your keyboard.
And, as an aside, I'd recommend looking at trackballs. Much easier on the
wrist.