Is this an upgarade from an old version/system to .net v2.0 . I would recommend, you take the approach of a regression testing. ie: this appilcation would be tested earlier and would be having, the earlier test cases right? You can take the same test cases and verify if the pass, when executed in the new system. This would confirm that the functioanlity remains the same or works just fine.
If this is not an old one's upgrade then you need to start right from the scratch, identify the different phases required(functionality, UI, Compatibility, user rights, Dirty testing, Acceptance etc..)Form the necessary checklist for each pahse, start out..
Im a newbie to this field, i welcome any suggestions and guidance from you.