Table layout problem - Firefox versus Chrome and IE7
I don't know about chrome, but I believe that IE7 requires an explicit "width: auto;" on elements for it to properly handle "min-width". This does not appear to be documented on msdn, however it seems to come up on google.
http://blog.throbs.net/2006/11/17/IE7+And+MinWidth+.aspx
http://msdn.microsoft.com/en-us/library/ms530820(VS.85).aspx
(Also, there are some constraints on using min-width with tables and colgroups, so what you're after might not actually be possible.)