I tried winnyp a few months back and found the same problems as Dan is getting. 7.28 nodes all seem to be pretty much anime and hentai as that's all I got when making a very general search. But this was back when it was released for only a couple months.
Sounds like you didn't read the readme and set it to connect to the older nodes...
oh and for winny6.66-7.1 the best cluster for H!P stuff is モーニング娘。松浦亜弥藤本美貴
I prefer the longer one I mentioned earlier. You still get a 30 match against people using your keywords, but an 80 or so one with other people using it. Seems to work pretty well for me, although I've had good luck with both over the years.
^ open/closed source has nothing to do with it. Freenet is as "safe" as you can get and it's open source. Share is safe mostly because the data and the traffic is encrypted.
Indeed, it's the network and protocol design that matters, not whether the client is open source or not. With share and ny there have been products for ISPs and what not available in the Japanese market that can read the protocols for a while now. See articles like
this one. Mostly just used for traffic shaping or straight out blocking.
And you should be aware that BitTorrent has pretty much 0 privacy or protection. Wouldn't matter if your client were open source or closed source, the way it's designed pretty much demands that you broadcast who you are and what it is you're sharing with it. If you're paranoid about legal trouble it's not a particularily safe p2p to be using.
Also: Mirc is neither a p2p program nor open source, it's just a shareware chat client that lets you send files. Not sure how that got on your list of open source p2p programs...