Ahh. I had an IE hack a long time ago that put this option into the right-click menu. I have no idea where that original site is anymore. Nicholas Roussos has some bookmarklets that wil automatically resize your browser to 640x480, 800x600, 1024x768 - superhandy for seeing what your website will look like at different resolutions.
More bookmarklets at Jesse's Bookmarklets site, such as a W3C HMTL validator, linked images, and linked pages.
via LifeHacker