There are others up here that are better at wiring issues than I am. Have you looked at the Dimension Engineering web site for instructions? I believe this is the manual for the one I think you have:
What part of the wiring are you concerned about? You connect the two wires from the first set of motors to the terminals marked M1A and M1B and likewise the two wires from the second set of motor to M2A and M2B. You would connect the motor Battery to the terminals marked: B- and B+ making sure you get the positive and negative correct. This wiring should have a switch in it to be able to turn the power on or off.
Since you mention wanting to use the sabertooth in RC mode. So you will need to make up two servo type wires with the three pin connectors at one end to plug into the BB2 IO pins 0 and 1. Assuming that the wire colors are Black/Red/Yellow, you would connect the black from both of these wire sets to the 0V terminal on the sabertooth, likewise you would connect the two Red wires to the 5V terminal and finally you would connect the two yellow wires with one going to S1(probably the one connected to P0 on the BB2) and the second one going to S2.
On the switches on the Sabertooth it looks like you need:
1 - Down
2 - up To select RC mode
3 - up (I think) lithium shut off
4 - down - to turn off mixed mode
5 - down - Turn off exponential mode
6 - Down - Turn on microcontroller mode - no timeouts no auto calibrate
Now again this is only my best guess at what you have.