Okay, so you can't clip externally referenced drawings in LT 2009 (although you can modify the boundary of a clipped xref), but you CAN clip every other type of referenced files, including DWF, and DGN, and images.
The commands are DWFCLIP, DGNCLIP, and IMAGECLIP, and they're all handily grouped on the Blocks & References tab of the Ribbon.
To show you how it works, I'm going to clip a pictures I took a few months ago in San Francisco (I still can't get over how steep some of those streets are.)
When you start the command, you're asked to pick the image to clip, then whether you want to turn an existing boundary on or off, delete the existing boundary (if there is one), or create a new one. I entered N for new, then P for polygonal. (It's more interesting than rectangular.) You can then pick points to create a polygonal boundary. The boundary will always be closed, similar to defining a polygonal selection window, and it can't be bigger than the image itself. When you're done, press enter, and the image will be cropped to your boundary.
Chances are you'd crop your images in a more logical and less random way, but this at least will introduce you to the possibilities.