…and suppose if I’m designing a pop-up window that fits the screen… should I leave the menu bars?
might want to read that first… i’d look into the most popular resolutions, 800x600 and 1024x768. so for width, no greater than 700x450 is what i follow.
Try not to use exactly 800 x 600 (or 1024X768) because we have scroll bars and top bars and a start menu on our system monitors that will cover up some of the popup.
You can find the exact best dimensions on google. Do a search and play around with the settings until you get something that fits both us and your site :).