Use the ‘onload’ event in the section of page B plus the JavaScript command window.open
Use the _self keyword in your JavaScript to launch somesite.com in the current frame. Note: if your Page B is not in a separate frame of its own, then your ‘somesite.com’ will launch in place of everything in the current frame. Therefore Page B needs to be a separate frame to the rest of the components (your menu, banner etc).
I do this all the time.Create a frame set with the top the left nav and the main frames. Have the nav frame open into the main frame and setup your links.