good day!!!
About your question, i think it is possible to save data on different sheets of excel. Have you tried to use ActiveX? You can use the "Automation Open" function of activeX to run excel application remotely. Through the use of "property node" and "invoke node", all properties and methods of excel can be controlled in LabVIEW including the writing of data on a specific sheets.
as an additional note, not all active x objects of excel 2000 are supported in excel 2003. therefore, better to decide what version of excel you will use so that you can have a flexible report generation vi.
hope these infos will help you. good luck!!!!