Ideally web pages/sites should work in any browser, on any computer (PC, Mac, Unix/Linux workstation etc.) at any resolution down to 640x480 at any colour depth down to 8 bits (256 colours). However 800x600 is often taken as a base minimum requirement for many sites and, in my experience, is a common minimum resolution these days. When designing web pages it's worth installing one of those Windows taskbar based resolution switchers (e.g. from the Windows Resource Kit or other third party versions) which allow you to quickly switch resolution (and other display settings) for testing without having to go through the Control Panel Display ****** all the time.