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?

>>1
It is possible with proxies.  Also, sane providers won't allow you to send packets with fake sauce address (at least which is not in your segment).