You can already view attachments:
DOC / XLS / PDF / TXT / JPG / GIF / TIF / PNG
For editing attachments, you need something like eOffice:
http://www.dynoplex.com/eOffice.shtml
(Although you do not need BES for this particular task, BES can be useful for many things -- you can get
Hosted BES for $10-$25 per month)