Try upgrading your BlackBerry to Version 4.0:
http://www.blackberryforums.com/viewtopic.php?t=1995
You can install the Rogers 4.0 on your BlackBerry 7290, for example.
(Just make sure to remove the VENDOR.XML file)
Your BlackBerry
should be able to view DOC / PDF / XLS / TXT / GIF / TIF / PNG / JPG email attachments, once it's upgraded to 4.0.