You can not hide your IP address from Internet sites using just software on your computer.... (or your router as rov suggests)
Hiding your IP address and then expecting websites to work would be like hiding your house and expecting the postman to deliver to it!
to address your points...
Hackers : they will just scan a range of addresses until they find one that looks interesting, you can't hide from that. but why would a hacker waste their time on you (no offense) what would they gain from it?
Forums: well no, it's not actually your right to hide your address from them, you are using their service, why should you have the right to use somebody else's services without complying to their rules?
The only way to hide your IP on the internet is to use a third party proxy server, but most forums will have already blocked most proxy sites and a proxy will do nothing to protect you from the theoretical risk from hackers.