Hiding and showing columns is simple in Reporting Services - each column has a "Visibility" property that can be set using an expression. The expression could be driven by a parameter, calculation or data and only needs to resolve to "True" or "False".
One way I use to hide and show columns is allowing the user to select which columns to show using a multi-value parameter (to do this, you must be running at least Reporting Services 2005 which introduced multi-value parameters). Here's my method, step-by-step:
Step 1 is to set up the parameter. In the "Parameters" dialog, add a new parameter...