I have a '03 pre-facelift x5, and unless things changed dramatically, all you need is a flat head screwdriver and some patience. You just need to pry the plastic tabs under the hood and pull the grill out.(FYI, grill is pulled off from outside of hood) The trick is to keep the tabs from clicking back to their locked position as you go around the grill prying them open. The chrome accent surround also detaches from the vertical grill bars. Putting a new grill in is as easy as pushing it on and pressing until the tabs lock into place.
I hope this helps,
Rui