IP Spoofing

Been trying to change the TCP Header Source IP-Address field in my packets for couple days now. But it seems to be quite hard. I need to do a HTTP Request with Spoofed Source IP-Address. If possible could it be done for Curl?

>>9
Also, sane providers won't allow you to send packets with fake sauce address (at least which is not in your segment).
Actually, sane providers won't give a shit what address you send your packets out with because it's not their job and they'd rather use the processing power of their routers for actually useful things instead of unnecessary filtering.