Excluding Tasks from Critical Path Calculation

NKumar2010,
To your explicit questions:
- Is there a way to select which tasks would be included / excluded into critical path calculation? Yes. (Setting aside the key difference between the collection of Critical-flagged tasks and the logic-defined "Critical path,") MS Project allows you to define the "Critical" flag according to a Total Slack threshold. Unfortunately you can only move that threshold upwards from zero. Any zero or negative-TS tasks will always be flagged as critical.  This is likely not useful.
- ...how does the linkages precipitate up to summary tasks ?
They don't (and should not). Logical restraints exist between specific low-level tasks (your WBS tasks), and these restraints are used to calculate early dates, late dates, and total slack for the tasks. With fully automatic calculations, summary tasks inherit early and late dates from their sub-tasks, and the resulting total slack for these summary tasks is only rarely meaningful. Avoid the temptation to make summary CP reports from summary tasks.  You typically end up with a bunch of parallel summary-task bars that are meaningless.

If your executives demand, then it may be most useful to make a summary-level critical path report using a specially filtered and formatted view that includes key WBS tasks and adds specially constructed "hammock" tasks to represent extended chains of critical WBS tasks.
Good luck, tom