Not sure if this is clear from the responses, so let me try to clarify:

Here's a terminal map. http://www.houston-iah.com/maps.html

C and D are attached. In fact, D1, D2, D3, etc. replace C1, C2, C3, etc....

When you arrive in Terminal B, follow signs to the Terminal Link elevated train-- it leaves within the secured area. DO NOT LEAVE SECURITY

The Terminal Link runs about every 3 min. and takes 3 minutes to the middle of Terminal C, within security. Follow signs to your gate- if you do leave from the D gates, you will be abel to walk from C gates to D gates easily.

The whole connection can be done in 10-15 min. if you keep moving. Wait until you're at your gate before you go pee.

Good luck!!