I experienced a similar issue, searched the web, and found this thread.
It inspired me to the process described below, leading to a solution which may be helpful to others.
First, I'll specify the problem as I experienced it:
On a Windows 7 machine working in MS Office 2003 or Office 2010 (I have both installed) I tried to display the Open Dialog box for a specific folder. It took ages (=45 seconds) to populate this folder. A further annoyance was that the was no hour glass or other sign of life during the 45 seconds. The folder is on a network drive.
Interestingly, the Open Dialog box opened promptly when I was working from a Windows XP machine.
So, I took a copy of the folder (to avoid annoying other network users) and systematically tried to trace down whether it helped to remove any subfolders or files from the problematic folder.
This process lead me to the culprit: A shortcut called 'Desktop', which referred to
"
\\SomePC\c$\Documents and Settings\xxx\Desktop"
This file obviously generates a timeout problem in MS Office under Windows 7, but not in Windows XP.
So this is a way to solve a problem that seemed most mysterious at first. Hopefully this information can help others.