No, Mail does not work with Newsgroups.
There are several newsgroup readers out there. I use the (now "old" version of)
Unison, from Panic ($29). Their recent upgrade to 2.0 was fraught with issues, but I believe those issues are now sorted (finally) and so I'd suggest you try it out and see how you like it.
As for "hiding" your email address, I'm not sure what you mean, but what a lot of people do is they have a "public" email address (let's say a free Yahoo account or something like that) which they give out on public websites that require it -- and a "private" email address that is only given to trusted people.
Then, everything sent to the "public" email is just junked.
Another good tip is to use
MobileMe or Gmail, as they both "trap" a lot of incoming spam before it gets to you. Finally, use the junk filter on Mail -- it works pretty well once its trained.