I've not seen this Private Browsing (Panther for me), but unless it connects you to a proxy, then it doesn't hide your IP address. And even if it does, that still means that single proxy has your ip address, recorded against what it proxied for you.
If you want to surf for your pr0n and not leave an IP trace, you need to find an anonymous proxy, set yourself up to use it, do your stuff, then not use that proxy again.
I can't remember the name, but on the PC you can get a program that cycles a list of known proxies for you; so that sequencial requests are proxied through different IP addresses. That gives the best hiding you're going to get.
Also it is possible to proxy your proxy (i.e. get your machine to ask proxy A, which asks proxy B etc.)
Whether any of this is available on the Mac? I don't know. But "anonymous proxy" and "open proxy" are the things you want to be looking for.
Be aware that this will cock up tracking cookies, since the cookie will relate to the proxy ID.
