I have 2 10g and 1 2.5 g for breeding guppies. 1 10g holds the parents the 2.5 hold the newborns, and the other 10g holds the guppies that got too big (i breed them for feeders for my cichlids).
Guppies will eat their own fry, so If you want the babies to survive, I would move them to another tank. For the first few minute after giving birth, they will be fine, but once the mother recovers, her babies will become dinner.
I have had the best sucess using breeders boxes (with the two sperate compartments, one for the mother, one for the fry). I will put the female in about a week for so before she gives birth. I have used the nets before, but the only reason (i'm sure) that she didn't eat the fry is because I was there when she went into labor, and was able to pull out the babies as they were being born.
Newborn babies will eat finely crushed flake food and BBS for the first few months of their lives, after about 2-4 weeks, they can also eat frozen or live daphnia.
HTH, if you have any other questions, i can probably help.