Most forums have rules against creating multiple accounts, do they not? And most bans usually have a good reason behind them. If you must change your IP address, a quick google search will bring up dozens of pages to show you how. And just a suggestion, though I don't know the entire story, consider not doing whatever it was that got you banned initially. If it's a temporary ban, just wait it out. If it's permanent, best of luck in not getting discovered and banned again.