Sharing window's internet with mac?

So recently I acquired an old iMac G3, and I installed 10.4 on it. Right now, I have an ethernet cable connecting it to the PC with XP, and I enabled sharing on both machines. Neither machine is detecting the other. I successfully did this before with a Power Mac with 10.4 and the same PC but with Windows 7. I do not have an airport card available for the iMac. I'm wondering if the iMac's ethernet port is dead, or more likely that I'm doing something wrong.

Thanks in advance.

Does anyone really not know?

What encryption are you using? An older model iMac will not be able to access WPA networks, only the much more insecure WEP.

For computer to computer direct connection you will probably need a crossover network cable.