you must get a BB specific to your frame and cranks. BB's have differnt shell sizing (width) which is normally specified by the frame manufacturer (or you could measure), you must also get a matching spline for your crank, i.e. octalink, square taper, isis. Finally you must get a BB which matches the threading on your frame, english, french, italian etc....

http://sheldonbrown.com/gloss_bo-z.html#bottom

p.s. why not order your parts from your LBS step by step as they could help you along the way and you would be supporting your local shop?