I'm not a fan of frames....in your case you have to scroll to really understand what the page is about, which is a big design no-no. I know you're trying to keep the ads visible at the top, but I would try something else. Maybe put the ads vertically along either side of the page and make them so that they travel with the user when they scroll (this is possible with javascript - google it).
Just like the fish said frames are not good. Any good designer will tell you that frames are not for pros. The disclosure "This Website Is Optimised For Viewing In Microsoft..." should be in the footer of the page not header. I'm not feeling the boldface of the top menu (o2, tmobile, about, contact) id have it just as regular not bold. Inside the frame, in the footer where it shows copyright Telefonica o2 uk limited, is that yours or...because it links to o2.co.uk?
The design itself is decent enough. The use of frames is ridiculous. I run my monitors at 1200x1920 (vertical) and this page looks ridiculous. I don't think they even sell 1024x768 monitors anymore. You should generally design sites to work with IE7+, FF3.0+ and webkit. People use their browser of choice, not yours. Also, IE8 is automatically pushed over Windows Update nowadays, time to update.