Here are two things I have found useful one of which may solve your question the other is only helpful for the simple setting of a starting point within your page for the cursor. These are ASP.net specific and are in VB
.net coding. I hope they help. I have tried to give some commenting for them and an example of where these bits of code are best placed.
This first portion shows where in your code you will need to place the function calls.
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.SetFocus(Me.tbPass) 'Change the tbPass portion to any of the text boxes in your code to make the cursor start in that box
Page.RegisterHiddenField("__EVENTTARGET", "btnSubmit") 'This will setup an event trigger that waits for either enter to be pressed and then redirects it as if it were a mouse click to whichever button or link you specify in this case the btnSubmit
This is the function portion of the SetFocus call, it could be placed in a header for use throughout a program or used in a specific page
Private Sub SetFocus(ByVal ctrl As System.Web.UI.Control)