Our cat was always indifferent to the guinea pigs, I think partly because they didn't run away like mice or hamsters do (don't know if that's the norm or if ours were eccentric) and partly we were never sure if that cat ever really knew she was a cat - she was very uncatlike. We had a garage with an upstairs and they had the run of the upstairs with a warm box to sleep in. They were engaging little critters. Dennett is right though - make sure you ahve 2 females unless you want 200 by this time next year.