Roger_Smith, the safest bet is to get a good newsreader (one downside to Outlook express is that it doesn't do native yEnc decoding; many binaries posted these days are encoded that way on the newsgroups, so you can't really use Outlook express).
Xnews is a free one, although the interface takes some getting used to. But once you have set up a connection to your ISPs news server, you can usually open whatever window to see a list of newsgroups your server subscribes, to, and just type "breast" in the newsgroup window. Most news readers will filter and show you only those group names that have "breast" in them, like
alt.binaries.nospam.breasts.natural
alt.binaries.pictures.erotica.breasts.large
etc, etc.
Usually, you can do a "get message count" option as well, and you'll see which groups have the most messages. Many messages is usually a good thing- it means it's an active group with a lot of people posting. When you start out, just try subscribing to several of them, making sure to only get message headers. After a short while, you'll quickly realize what groups are good for getting stuff you might want.
You might also try:
alt.binaries.multimedia.erotica (for general porn)
alt.binaries.nospam.multimedia.erotica
alt.binaries.mpeg (not terribly active all the time, but it's where I tend to see Christina Model movies, and a couple of Yulia movies, posted on occasion)