Beg as in sit pretty? I just thought that to Jo the other day. I got her to sit. Then I'd say Sit pretty (or beg whatever you like) then I'd take her paws and push her to the right position and say it again, then release as say good dog!! and LOTS of praise. If you want trainin to be easier, make it fun for the dog so it's not bored. in my case, if food is involved. To teach your dog to walk on its hind legs (I never did this so i duno if it works) I would get it to stand on its hind legs (like hold a teach in the air) Once it can ballance for a little while standing still, start to move back a bit still holding the treat, say what you will to the dog, and if he/she does it, give the treat and praise. Don't spend to long on it at a time, dogs will get bored and loose attention. It takes time so goodluck!

Another way to get the dog to sit pretty or beg, would be to let it ballance on your arm till it gets the hang of it :]