Heres how
You must be running Media Centre on your xbox 360 to do this.
Boot up media centre and go to settings.
Select Help and then go to the Community Forums section on the help screen.
When the site boots up click allow and you will be at the microsoft site
Here are the controls for your 360 controller
Y brings up the text screen input what you wish to search for or what site you want to visit.
Double click middle of Left Stick to move your browser into text boxes
Right stick moves the page up and down.
Still working on how to get the address bar up.
Feel free to add your other discoverys