Excel 2007 : Locking Sheet But Allowing users to group

[AlexApazidis]

I am trying to allow the users of a sheet to group and ungroup as they see fit certain Columns, but the entire sheet and all the cells cannot have the formulas changed. The columns represent months (jan thru dec) along with Qtr intervals. I only want the active quarter (i.e jan- mar with Q1). I can't have seperate tabs because each sheet rolls upinto a disrict, and the district workbook needs a shhet for each unit and a summary for the district. Any Ideas?!