I came across a nasty Outlook 2007 bug this morning whilst building an HTML email for a client. When I viewed the email without downloading the photos in Outlook 2007, the table cells widths were all correct. However, upon downloading the images the table re-sized itself to an arbitrary layout. Very frustrating!
I had used spacer gifs throughout the html to force the right widths, but here Outlook 2007 was resizing some of those gifs to suit itself.
Anyway, after an hour of playing about, I finally fixed it. If you experience the same problem, create spacer gifs that are the exact size as stated in your html.
I know it is a faff, but this does seem to force Outlook 2007 to behave properly. I can only assume there is some glitch with the way it renders incorrectly sized images.
Hope this helps others with the same problem.