You can use 120x600 or 160x600, these adsense formats can provide 4 or 5 ads. The way I find the easiest is to use a plugin called "Quick Adsense" that allows you to add adsense ad code, banners codes or just about any other else such as an optin box in the sidebar and in your posts. You can adjust all the settings in the "settings" section of the your wp admin. Mike