Please go kick that guy in a sensitive area for me.

I'm so glad your neighbor found the poor little guy in time.
Ferrets are fun pets if you can deal with them. They need a lot of out time at this age. I'd say at least 6-8 hours to get all his energy out. That doesn't have to all be you+him playing. Ferrets are perfectly happy wandering around getting into stuff and checking out the room. Some people go for overnight out time with small romps during the day/evening with attention and cuddling. The safest thing to do is have a room or area of the house that's gated off and designated ferret land. This way you can go around and make sure everything is safe and then let him out there. In addition to what LS said about destruction and chewing electrical cords, you need to pull furniture/cages away from the wall enough that they won't fall down the back and get stuck, and remove anything soft enough to chew chunks out of (shoes, rubber anything, soft plastic...). Surgery to remove the bits from his intestine is expensive. The other big problem is poop. Ferrets are not ever going to be litter trained as well as a cat, but some training is SOMETIMES possible. Ferrets tend to go in corners, so if they have a favorite corner they like to use, you can put down a corner litter pan and hopefully he'll use it. Mine was not trainable outside her cage. She'd use any old corner/side of object and would even go in the middle of the room. Short of plastering the entire floor with litter boxes, not much I could do. They don't look for a litter box, they just kinda go where they feel like it, and if a litter box happens to be there, it doesn't end up on the floor. Carpet is definately not your friend here. Try to make his "out room" hard flooring if possible or put down linoleum and newspaper in the corners to make cleanup easier. Be prepared to clean up a ton of poop spots either way. You also don't want carpet because ferrets "dig" and will shred the carpet down to the plastic threads.
Also be ready for the financial commitment if you decide to keep him. Ferrets are expensive beasts. Their food is expensive, and their medical bills are huge because they're "exotics". My routine vet bill for checkup, shots, and melatonin implant (adrenal preventative) came to about $200. Her final emergency vet visit was estimated $2-3,000 for overnight stay but she went downhill so fast, she didn't make it to most of the expensive tests. Even still, storing her overnight in an oxygen cage and bloodwork came to $800, and they didn't even try to fix anything. It's a good idea to find your exotic vet(s) and emergency clinic that sees exotics and ask about their prices. Your vet may charge more or less, I just wanted to give you an example. Ferrets are accident prone and you are guaranteed to have disasters no matter how careful you are. It just happens.
If you do keep him, look into getting him a friend. Ferrets are much happier with a playmate or 2. They cuddle, wrestle, chase each other.... My advice is to look up petfinder and see where your local ferret rescues or humane societies with ferrets are. Bring your ferret along and see how he gets along with the new guy/gal. Let them out together to get acquainted and see if they play together. If the somebody jumps on the other guy and starts pummeling him, keep looking.... I volunteer at a MD ferret rescue and we mix in single ferrets that are 4-5 years old and never lived with another ferret in their lives. They usually take quickly to living with other ferrets no matter how old they are. Your big problem is a really dominant ferret. Some ferrets will just beat the stuffing out of every other ferret they meet for fun. My ferret was like this and she had to be single. Nobody wanted to live with her. She did not leave them alone.
Ferrets are awesome pets and I love them. They're not for everyone and they are not easy pets, which is why we have so many abandoned and neglected ferrets. If only other people were as good as you about looking up the pet's needs before taking it in. There should be a sign on pet store ferret cages " WILL POOP ON FLOOR, BITE YOU, AND DESTROY YOUR STUFF." It's funny how the people selling them don't seem to ever mention those points....
Other good sites:
Care tips:
http://www.rockysferrets.com/ferret_tips/index.htmlGood forum:
http://www.ferretvillage.org/