If you have an Microsoft Sharepoint 2010 server and Internet Explorer 6 clients, you will face some horrorible layout problems and SharePoint will not be usable by the clients.
The only way to solve this problem is setting SharePoint 2010 to the visual style of SharePoint 2007.
This process is called "Visual Upgrade" and is well documented by microsoft at: http://technet.microsoft.com/en-us/library/ff607998.aspx
This is in my case a very well feature for an "enterprise bug". Because only in very big enterprise companies you will find an Internet Explorer 6 environment. You may think this will not happen? Believe me still at the time of this post Internet Explorer 6 is still present in some large companies.