Yes - this is possible in V4 using the crop visual FX as described below...
OR
For video input only - you can use the 'crop' features in the video input controls window. This will allow you to crop each of the 4 sides of the video inputs Top, Bot, L, R. (commonly used to get rid of noise around the edge of pictures).
You can still use the Crop FX on each layer - on top of the video input crop (if you if you really need to...)
If you're still running V3 - download V4 and have a look to see if it will do what you need it to. Let me know if you want a quote to upgrade your dongle
Simon