Been mom to guinea pigs forever! If you have any questions, just ask! Just to note...While pellets are a big part of their diet, a constant, fresh supply of timothy hay is absolutely necessary to maintain a healthy digestive track. No alfalfa hay; only for very young pigs or ailing pigs. And there a lot of junk pellets to be had, but the best is sold by Oxbow. They have great care info on their site too (2nd link)

http://www.oxbowanimalhealth.com/

http://www.oxbowanimalhealth.com/pet_care/guinea_pigs

They love fresh greens (the darker the better, though go easy on the spinach) and fresh fruits in limited quantities are fine. They LOVE fruit, hehe. Vit C is essential, and while they may get enough through their diet, most vets recommend a supplement. All pet stores carry vit c liquid that you can add to the water bottle.

Hope this helps!