Suppose i registered to a certain forum (such as cplusplus.com), i provided the information required (email address and whatnot), what will appear to them behind the scenes? Can they track my ip and do some crazy things like find out where i live?
You give your IP, they can only know an approximation of your location
(Your ISP will choose which position to give out. I usually have a position near 150km from my actual position. Wireless (mobile) internet is usually more precise. More reliable is the country you live in: I always get Italy, from both wired and wireless internet)
An IP is simply a number, after all, and it can't be as precise as GPS tracking.
Note: You give your IP to ALL the websites you browse. --ALL.
Only exception is through a proxy, they will get the proxy's IP instead.
Google for HTTP Proxies.
I use AnonWWW: http://anonymouse.org/anonwww.html
Only cons is the popup ad, but I do understand that, since you do not pay for the service.
Note: Ad-blocking software won't work as expected, since ALL content gets redirected by the proxy.
Geo-IP databases can only give approximate locations, and as EssGeEich said, it's less accurate than even triangulation through cellular towers.
In order to find you where you live, whoever has your IP would need to get in touch with your ISP and ask them what building your current IP was associated with at a given time.
Needless to say, ISPs don't give out this information to anyone but the authorities, AFAIK.