ASP.NET forms authentication against AD

Hi there,
I have struggled with forms authentication against AD.  I have a working asp.net 2.0 code that works on IIS 6 in Classic Mode.  Things get complicated because our live serve is II 6 and development server is II 7.5.  I wish I can upgrade live server but it’s not possible at the moment.  So I need some help with making ASP.NET 4.0 Forms authentication against AD work on IIS 6.0 in integrated mode and on IIS 7.5 in integrated mode. The code should create a non-persistent cookie that will disappear as soon as browser is closed. Cookie will be used to authorize user.
For some reason there is very little documentation from Microsoft itself authentication against AD for ASP.NET above v2.0.  
The reason I’m looking for code that will work in IIS integrated mode because sooner or later we will be moving our live server to IIS 7.5 and Classic mode might disappear from IIS. Integrated mode is more efficient than Classic mode ...