If you're a googlepages user and you want to add the adsense code to your page, you'll need to save the file you have to your machine and add the code. Once this is done, upload your page as a .htm or .html file and then you'll be able to link to it from your GPC files. Once this is done, it'll take a short while for AdSense to figure out what your page is about and you begin the task of getting to grips with AdSense.