When you write code for a browser-enabled form, it runs on the server. This is why using WinForms makes no sense for browser-enabled forms.
Since you cannot use WinForms (or any sort of custom UI, for that matter), your best bet is to show in-line UI by using conditional formatting on a section.
David Airapetyan / Software Services ArchitectQdabra® Software / Streamline data gathering to turn process into knowledge