We got a male lab puppy he is 3 months old. And a friend wanted to get rid of a female boxer that is 10 months old, that has been spayed, if she couldn't find someone to take it in then she would have to go to the animal rescue league. So we just got her yesterday. First we took our lab puppy to see how they would get along. They seemed to get along fine. But when we got them home the lab puppy has decided to keep attacking the much bigger boxer puppy and won't stop. When we take them on walks the lab keeps trying to bite the boxer's ankles. And @ home he keeps pounching on the boxer when she is laying down trying to rest and nipping her. We are trying to make sure they both get the same amount of attention. And the boxer is very calm but now when the lab goes near the boxer they both keep nipping @ each other and won't stop. They don't seem to be bitting hard or anything but we can't get them to stop it. Any suggestions??
Thanks:)

They will probably out grow it but maybe you should try and figure a way to keep them separate enough that they can not get in biting distance of each other

For any unwanted behaviour I would suggest the use of a haltie.

I think you have a great combination and male and female... esp since she is spayed.
They are probably just playing when the bopxer gets tired of the abuse she will put him in check.
Now if you are only keeping her because of pity, there are many great boxer rescues that will gladly take her and put her in a forever home. They may ask you to drive her to them but they also have volunteers that will come and pick them up no matter the distance... so you do have options other than keep her.
I am of the opinion that 2 dogs are better than 1 any day if you want and are able to have them.

*edit* try to stress to your friend that animals should not be treated as if they are disposable, that they have feelings too. She should really think hard about ever getting another dog.

This sounds like completely normal behavior (in fact as I write this my own kitten is attacking my older cat in a very similar way). The older dog will eventually let the younger know when enough is enough. Lots of exercise and training for both dogs will keep them both occupied and help you keep control as well.
Couple of rules for dog play: You are allowed to make a lot of noise, you can bite and nip at the head, ears, feet and butt.