SharePoint V3: Error: Your Client Does Not Support Opening This List In Windows Explorer
Users who are running IE 6 are are unable view SharePoint document libraries in Windows Explorer view. Users who have IE 7 do not have this problem.
IE 6 doesn't support Windows Explorer View when the URL is more than 100 character URLs. If it is not feasible to upgrade to IE 7, there are a couple KB articles that explain the details and provide instructions to obtain a patch that remedies this issue.
When you try to open a folder in a Windows SharePoint Services 3.0 document library in Explorer View, the folder does not open
You cannot access Word documents by using Outlook Web Access on a server that is running SharePoint Portal Server