I would like more specifics on how a 580EX II would work on a Nikon D5000 and if it is even worth it.

This is the scenario, I have available a Canon XTi with a 580EX II for buying; I own a D5000 Nikon and a SB600 flash.

I know the 580EX II is equivalent to the SB900 Nikon and would love to know if it is possible and worth to buy that setup for the flash alone? Would that work with the SB600 as an external in case it cannot replace it?

I am no expert and trying to learn the trade but I can tell, by my short experience, how much I admire you guys out there, capable of just picking up any camera and doing such a wonderful job. My God! So many little details to make a picture perfect!!!

The kit I am talking about is selling for 650U$ used but in great shape. The XTi comes in great condition and has no signs of wear. The flash looks brand new.

Any suggestions will be so welcome. Please forgive me for so many questions but I gotta rely on you to be able to make a wise decision. Note: I even wondered if it would be worth to sell my D5000 and keep the XTi/580EX II setup but, reading, I am not sure would be a wise decision.