The basics of the 3.0 are:
Pull the splash shield off the front bottom. Stick a pan under there to catch coolant. Pull the clutch fan, that is discussed elsewhere in detail. Cover your belts, pop the hoses, catch resulting coolant. Pop the plastic rivets that hold the top of the radiator shroud, detach the electrical connector that lives on the left side of the shroud (looking into the engine bay), lift it up off it's tabs and then pull it out or drop it out the bottom.
RealOEM.com BMW E53 X5 3.0i Expansion tank, manual transmission
Then there are a series of bolts that hold the top radiator support cover on. Pull those. I would leave the expansion tank attached if you can. It's probably a good idea to replace that if you replace the radiator anyhow - they crack and leak eventually.
Then there are 2 expanding plastic fasteners that engage through square plastic holders that cradle the top of the radiator. Remove those. I think there may be a couple plastic rivets at the bottom of the radiator as well, but I cannot remember.
RealOEM.com BMW E53 X5 3.0i RADIATOR/FRAME
Anyhow, that's the quick version, I am sure someone else can fill in the blanks.