Is there any way to change the width of the overall site. Thou I know it is not recommended i am using <iframe>'s and the right half of the shopping cart is out of the iframe. Maybe through the css. But where?

Edit your DEFAULT.CSS file - look for "/* Main layout width */" around line 46 and change the width in pixels. There are three you need to edit. Unfortunately this will be overwritten every time you upload your store. Someone had suggested that as long as you don't make and changes in the appearance of your site you could save a back up copy and simply upload it after updating your store.