By using ICS you could do such a thing. Here's an example. http://www.microsoft.com/windowsxp/using/networking/expert/bowman_02april08.mspx

But be aware I will not answer queries about how to do this or give any "step by step." Here's why. Because this is advanced networking you must understand what you are doing or else it will break and cause too much grief for all involved.

But it is possible.
Bob