What airline are you arriving in Terminal B? Continental Express?

B and E are not connected in IAH. You cannot take the "cart".

A helpful post:
Here is one post that can be of help to you.

Map of IAH terminals:

IAH terminal map

recent thread on related topic:

Here is a recent thread about IAH terminals (not specifically on your question)

This thread is better suited for the "south" or the "continental airlines" forums. the moderators might move it.