>In a form, I have a second button used to execute an operation. The first one is used for the save. Both are submitting the form. How can I detect which button was pressed?

Each button has it's own Click event - you can just hook up a handler to the second button's event, eg.

<asp:Button runat="server" id="btnSave" Text="Save" onclick="btnSave_Save"></asp:Button>

In the codebehind:

Protected Sub btnSave_Click(ByVal sender As object, ByVal e As EventArgs)
' Code to respond to click here
End Sub