Ok, I went through the forums over and over looking for a answer. i also looked around the net and what I found was this. And it worked for me.
I am using Windows 7 64bit with Norton's Internet Security 2010.
Open the "Network Security Map"
Find your Xbox in the map (make sure your Xbox is turned on and connected online)
Under "Trust Level" select "Edit".
Change the trust level to "Full Trust"
Save settings if given the option
I am not saying this will work for everyone but it did work for me and know I can access my laptops media center from my Xbox 360.
Hope this helps someone out.