You should do lots of research before you decide if you want guinea pigs! You can't want a pet until you know whether it suits your lifestyle or not.
Guinea pigs are social and should be kept in same-sex pairs. You should get 2, to keep each other company or else they get pretty lonely. Even if you plan to play with it lots, it will spend the majority of time in a cage, all alone.
You need a large cage. Guinea pigs require a lot of space, and cages can be quite expensive. I suggest C&C cages. They are best recommended for guinea pigs. It should be one level, since guinea pis are not very good climbers.
http://www.guineapigcages.com/
You'll need to choose a safe bedding. Lots of owners use fleece: http://www.google.com/imgres?imgurl=http://www.guineapigcages.com/photos/data/544/medium/86503D65.jpg&imgrefurl=http://www.guineapigcages.com/photos/showphoto.php/photo/7272&usg=__NlmeKp968FAmEpz48L9TBYw7lJk=&h=449&w=600&sz=36&hl=xx-pirate&start=15&sig2=VzHLdWfB66I1iExLq7U_qw&zoom=1&tbnid=8gjpVMjH824h9M:&tbnh=109&tbnw=154&ei=ESrtTYKWLYXl0QGt_6yeAQ&prev=/search%3Fq%3Dfleece%2Bguinea%2Bpig%2Bcage%26um%3D1%26hl%3Dxx-pirate%26sa%3DN%26biw%3D785%26bih%3D322%26tbm%3Disch&um=1&itbs=1&iact=hc&vpx=481&vpy=17&dur=4688&hovh=194&hovw=260&tx=199&ty=140&page=3&ndsp=8&ved=1t:429,r:7,s:15&biw=785&bih=322 which can be washed and reused to save money. It is also not messy and very safe for your piggies.
Aspen and Carefresh are other safe beddings. Avoid cedar and pine is iffy, so best to stay away from that too. These can harm your pet.
A guinea pig's diet requires pellets and hay available 24/7. These should be Alfalfa based until the pigs are about a year old, then switch both to timothy based. Each guinea pi needs 1 cup of veggies per day, and a vitamin C supplement daily. Water needs to be refreshed daily.
Guinea pigs are shy and timid by nature. They are often skittish and jumpy when being picked up or taken out of their cage. Guinea pigs are usually a lap pet. They are lazy and like to sit around while you pet them and give them treats. They are not usually very active or entertaining to watch. They require time out of their cage each day.
You should purchase your guinea pigs from a breeder or shelter, and not a pet store. Pet store rodents are usually mistreated, not socialized, sick, and/or pregnant (if you get females). A breeder will ensure healthier, happier guinea pigs that are more comfortable around humans.
Different species should never be mixed. Hamsters are solitary animals and don't like having friends, especially of a different species. Your hamster will attack the guinea pig, and one will likely be injured or killed. Being around each other will stress them both out tremendously. Don't let them interact at all. Your hamster will be fine on its own, and your guinea pig needs the company only of another guinea pig
Good luck! Hope I helped!