Good PAge regarding the use of masterpages
http://www.odetocode.com/Articles/450.aspx

Also discusses the adding of Javascript to a page using the

Dim script As String = “[Label1ID].innerHTML = ‘boo!’;”
Dim scriptKey As String = “SayBoo”
Dim addScriptTags As Boolean = True

Protected Sub Page_Load(ByVal sender As Object, _
ByVal e As EventArgs)

script = script.Replace(“[Label1ID]”, Label1.ClientID)

ClientScript.RegisterStartupScript( _
Me.GetType(), scriptKey, script, addScriptTags _
)

End Sub

usemap

URL

Defines the image as a client-side image map. Look at the ‘map’ and ‘area’ tags to figure out how it works

STF

http://www.w3schools.com/tags/tag_img.asp

ASP.NET:
http://www.codeproject.com/KB/aspnet/Detecting_Session_Timeout.aspx

‘HOMEPAGE’ in the above example could be referred to as the login.aspx

AJAX:
http://geekswithblogs.net/AzamSharp/archive/2008/01/05/118269.aspx

JAVASCRIPT:
Detecting Session Timeout and then using javascript to provide a warning regarding timing out
http://classicasp.aspfaq.com/general/how-do-i-warn-people-when-their-session-is-about-to-expire.html

SQL:
Using SQL to maintain Session information:
http://classicasp.aspfaq.com/general/how-do-i-count-the-number-of-current-users/sessions.html

Using the Ad-rotator control to server blank png to renew session.
http://forums.asp.net/t/1191063.aspx

http://www.dynamicdrive.com/dynamicindex17/indexb.html