An x-pen is one of those exercise pens where you can put there bed and toys and pee pad in if you can't watch them or if you're away from the home. They are also good for outside and to close off a large doorway where some gates won't fit. We use it for that in our house sometimes and it's very handy.
Here is a picture of an x-pen with this link. Hopefully it will work.
MidWest Pet Exercise Pen - PetSupplies.com
As for positive reinforcement I've heard some people will give treats but I never did with my girls. I find that yorkies really respond well to praise. So if I would see them go on the pee pad or when I had them outside I would just go crazy saying good girl, over a few times and clap. Ha ha ha...people probably would think I'm nuts if they overheard me but it works. I will also say the word pee pee to them or poo poo although some will say potty when they go and now they all go on command when I say this. The reason I say the two commands is because the girls are so smart they know one from the other.
Even now when my girls go outside I still tell them good girl Mica, Maggie or whichever one is going. I constantly reinforce this with them.