.NET 3.5 is already there in windows 8.You just have to turn it on...!!!!
Just follow my procedure :
*Go to CONTROL PANEL>PROGRAMS>PROGRAMS AND FEATURES>
*In that click on ' TURN WINDOWS FEATURES ON AND OFF '.
*Click on box showing .NET FRAMEWORK 3.5
*It will download some neccessary files.
*That's it you are done..... .NET framework is installed ...!!!
Hope I helped you bro...Cheers.