gnutella is a pretty good kazaa replacement, but I still find kazaa on my windows box has a better selection. gnutella is just as good as kazaa in technology, but the network of users is not as big.
There are a billion gnutella clients out there, depending on your preference for gui, command lines, or your preferred windowing system. I'm sure you can google for it and find one you like.
Also, for gaming on your Linux box you can't beat MAME and a few hundred classic arcade games.