Theres another way but this way is how the cops track you down. They contact the forum admin then the forum admin gives ip address then they find out which internet company ip address after they found out which ip address the internet company then the cops ask who used this ip at this time then the internet company gives the cops the address your name etc. Then the cops come to your house and knock on your door or kick it down.To prevent the cops getting you just give a fake address to the internet company.(it will not100% work it just delay them finding out where you are) they can find you out if you have cable the find out which cable has the ip if you have adsl pretty much the same thing dial they can probably find you where you are dialing from.But i don't think the cops will get this much trouble just to do this it will take lots of warrants,negotiating etc it just takes too long.
Theres lots of ways if you put your real name (just the name) on the web you can actually find out there location umm its called *cough* whitepages.
Pretty much all you need is the ip to actually find out its location.
To protect you from getting track down get a proxy server thats how hacker don't get tracked down easy because they hack into another person computer and frame the hacked computer and control the computer and make the computer do all there dirty work.When the cops come knocking it won't be the hacker.
WHen you get the ip you can do a i think its called whois and you can get there internet service location that would narrow your search on the person down.But overall doing all this will require a lot OF TIME and you probably won't bother doing it unless you desperately need to find out the person.
I guess thats cover it all i think they might be other methods?