Also, most cats are very good around guinea pigs. However, because this is a kitten, I wouldn't let them have much actual contact with the guinea pigs just yet as they tend to be very playful and could accidentally hurt the piggies. When they get a bit older though, if they don't have a very high prey drive (as in they aren't the kind of cat to instantly want to hunt every small animal/moving thing in sight), you could let them interact with supervision. Never, EVER leave the cat with the piggies unsupervised. No matter how well they seem to get along, it's just reckless and irresponsible to risk their wellbeing.
Otherwise, my cats seem to either like or fear Bob...Mr. Jinx could care less and lets Bob climb on him so long as he doesn't nibble his paws. Tinker Bell is fascinated by him but gets really upset if he tries to run into/under her and almost swatted him in the face once so I have to keep a close eye on her if she's in the room with us, and Edgar seems to like Bob's company but the other night Bob was chasing him around and rumbling and harassing him and Edgar was really scared about that.
Otherwise, Edgar's probably the best cat around Bob...he never tries to follow him or bother him, he just lays there and watches him and sometimes they sleep next to each other. So from personal experience (as believe me, I was just as freaked out and worried about the cats with the guinea pigs) with supervision, they'll be fine. But if you see your cat visibly bothering them or stalking and behaving as though they are hunting them (body low to the ground, butt wiggle preparing to pounce, tail low and twitching) theeen you should be concerned. Don't be alarmed if the cat wants to investigate the piggies, and just let it happen. Don't punish them for being curious, but interfere if they are actually distressing or hurting or being a potential threat to the piggies.
Otherwise, best of luck, and I'm glad you're getting a kitten--cats are wonderful animals and I can't even imagine life without one