<p>Hi I'd like to schedule an existing job in the Sql Server 2005 agent via C# code... i.e. when someone clicks a button on an asp.net web page.</p>

<p>How can I do this?</p>

<p>Thanks!</p>

Have a look here:
SMO Job Class
The
SQL Server Management Objects (SMO) Class Library
lets you do practically anything programmatically in SQL Server.