thanks guys.. so it sounds like i can keep my crank as is at 53/39 and add a 11/34 cassette to the back + new deraileur.

so, just to recap on the things i need:
Shimano Deore XT CS-M770 9-speed Cassette 11/34
Shimano Deore M591 SGS Rear Derailleur
9 speed Ultegra chain (can I still use my existing one since I still have the extra chain left over from last time)
In-line barrel shifter (where can i get that on performance?)

Anything else i'm missing? Do I need to change the shifter cables?