+2  A: 

You might want to take a look at the ScriptManager - CompositeScript feature... http://msdn.microsoft.com/en-us/library/cc488552.aspx
which can be used like this:

<asp:ScriptManager runat=”server” ID=”ScriptManager1”>
<CompositeScript>
    <Scripts>
        <asp:ScriptReference Name=”MicrosoftAjax.js” />
        <asp:ScriptReference Name=”MicrosoftAjaxWebForms.js” />
    </Scripts>
</CompositeScript>

Note that this is an ASP.NET 3.5 feature.. so if you are using at least 3.5, you will have access to this..

markt
A: 

I recommend you read this article which talks about the same thing you've asked.

http://www.codeproject.com/KB/aspnet/fastload.aspx

this. __curious_geek