megadan's post is right on the money.
How you hook it up all depends on what you're trying to do. I'm not sure how well the POD will do in the effects loop (i.e., Send to the POD input, and Return to the POD output). It might be unpleasantly overdriven if it's not designed for that level of input. No risk of damage, but it might not sound right. Give it a try and make adjustments as needed.
If you're just using it for effects, then simply run it into the normal input of the 2001RB, on the front of the head. If you're using it as a preamp, plug your bass into the POD input and the POD output into the "Return" jack. That'll bypass the 2001RB preamp. But if this is what you're planning to use it for... are you sure you wanted a 2001RB, or did you really want a plain poweramp?
