Actually, I don't see that you can "save as" excel from the reports in Test Plan. You can save as a text file and wrestle with that.
You can get into the folder that contains the tests that you want to put into excel, switch from Tree view to Grid view and then export to excel that way. However, you will not have your test steps in the grid, so the steps won't be exported this way.
Sathya, can you give more information on what information you are trying to export?