Samoi,
Another thing that can arise with bb is threading - English or Italian. It's easy enough to tell. Italian threading both sides thread in clockwise, ie, "normal". English, one side threads in clockwise, one counterclockwise. Also make sure the crankset and bb you purchase are compatible. Modern Shimano cranks require a modern splined-spindle Shimano bb, and the Shimano mtb spline is apparently different from the road spline. Older "traditional" cranks use a square, tapered spindle. Other than Campagnolo, the tapered square spindle is almost universal, ie, you can mix and match bb and crank brands. Campagnolo is also a square, tapered spindle, but the taper is slightly different so you must use Campy/Campy. For the most part you can mix models with Shimano. For instance, use an Ultegra bb with a 105 or Dura Ace crank. In fact, many recommend using the Ultegra bb with the DA crank because the Ultegra bb is more durable. Forgive me if you already know all this; just trying to help.
Regards,
Raymond