Originally Posted by JNG330
I'm planning to buy a new shimano xt rear derailleur soon. My question is will a 8/9 speed rear derailleur works with my 7 speed cassette/shifters? I think i read somewhere that it will work but just want to be sure
No problem. There's actually no such thing as a "9-speed" or "7-speed" derailer, that's just marketing hype. Derailers don't care how many gears there are.
See also:
http://sheldonbrown.com/speeds
Sheldon "No Problemo" Brown