The VSTS 2005 Forward Compatibility Update is now available. It is more focused on development scenarios. For administrative, project management and test case scenarios, the use of Team Explorer 2010 is recommended in the side by side configuration.
VSTS 2005 Forward Compatibility Update - KB979258
VS 2005 Side By Side QFE for Office Integration-KB946075 on Code Gallery
VS 2005 Side By Side QFE for Office Integration-KB946075 on Connect
Support for Test Management and Office Integration from Microsoft Project or Excel requires Team Explorer 2010 side by side with the 2005 client. You will need to install the Office Integration side by side QFE for Excel and Project scenarios. For example, the Office Integration Add-Ins for Excel and Project can be launched from 2005 but will have 2010 functionality when side by side. Similarly, test cases can be published from 2010 Build Automation when side by side.
It is important to make sure that VS 2005 SP1 was installed after Team Explorer 2005. The proper order of install should be VS 2005 + TE 2005 + 2005 SP1 + 2005 Forward Compatibility update.
If you have installed everything in the right order, you will be able to see the port and protocol have been grayed out when you have the URL path to the 2010 server typed in as shown.
If you are not seeing the port and protocol grayed out, uninstall the update, reinstall SP1 and then reinstall the update.