http://www.aracnet.com/~seagull/Guineas/careguide.html
The above link is a wonderful site for information and care.
I took in an adult Guinea Pig a couple of years ago from someone whose kids were allergic. They kept the poor little guy in the basement by himself.

He is now about 3 1/2 years old. He is very sweet.
It is really important to read up on their diet and housing.
Mine primarily eats, Timothy Hay, Fresh Veggies and a small portion of alfalfa pellets. Guinea pigs should not be fed a huge amount of the pellets because they are know to cause bladder stones. Mine just a bladder infection recently so he was put on a high water content diet. He has improved greatly since then and is back to his old self. He loves his fresh veggies and fruit. The above site discusses diet and has a list of the appropriate fruits and veg that they can eat.
Hay is a good time occupier for guinea pigs. They love to eat and it keeps them occupied since they graze all the time. Don't get the chew toys that that are made of seeds and honey, etc...Many of these sticks contain pieces of corn or sunflower seeds which can cause them to choke. Same goes for pellet food with seeds, etc...
As for bedding I avoid cedar at all costs. I use Aspen for his bedding. Cedar bedding can cause severe skin rashes or severe respiratory problems in small animals. My little guy has some skin problems when I first got him that cleared up once his bedding was switched. I also found that aspen doesn't make me sneeze, unlike cedar. Aspen is more expensive, but healthier for him in the long run.
Guinea pigs are really social animals so if you could get two females they would keep each other great company.
While young, get them used to having their nails trimmed. I've also bathed mine on occasion when he gets messy. He's so good about it. I used a small animal shampoo.
He/she should also have a private hutch area or plastic igloo that they can hide in. They like those small animal huts for sleeping and keeping warm.
If you have any more questions post them here
