At the
VirtualDub 3rd Party Filter website.
Specifically, you're looking for
Smart Resizer 1.1 filter.
Here's a screenshot of the settings you need for a landscape-view video (also requiring a Rotate filter, obviously). For profile view, use a width of 240 if you want the full screen, no skin/controls. Or 236x160 to keep the skin/controls visible.
The filter shows the original (input) height and width, and when you enable the size calculator, the new height/width is displayed at the top in the disabled editboxes labeled 'new height/width'.