The reason you would want to hide an IP address is usually not a good one.
You need something called a proxy server, which shouldn;t be that hard to find. I don;t know one off hand.
I must warn you though (as an EF bro) that if you are going to do something that attracts law enforcement personnel, you can nonetheless be easily located.
when a packet leaves your computer, it has an IP address, but it also has something called a MAC address. This source MAC address is constant because it is burned in to the network interface card on your PC. Your MAC address cannot hide behind a proxy server. it is hardware, an IP address is software.
A router will change teh destination MAC address of your packets, but not the source.
Just letting you know.