I don't think this is a WordPress issue - more of a CSS copatibility issue with IE7 or older. However I need someone to explain the issue and more importantly how I can fix this.
I have a web site (www.yogakevala.com) where everything displays fine in IE8+, Firefox, Chrome etc, but IE7 displays the menu vertically instead of horizontally. I am using a modified version of the Twenty Ten theme and changed things like padding, margins etc in the header.
Now I have compared the original files to the modified ones and I can identify the changes - however its impractical to test each change to see if it affects the display.
I have also seen this issue mentioned in other threads but I have not found a satisfactory fis or explanation - can anyone hemp me pin this down?
Also HTML validation may help but again I doubt if that is the issue.