It might be that Migration Assistant just won't work any longer with a drive from an "OS that is that old".
I don't think he got far enough to draw that conclusion. He said "I do see the g5 but I can't open it or anything". That indicates the ethernet connection is working, because he can see the G5 on the network. But he can't open the shared disk. So I think it's likely that file sharing has not been properly configured on the G5. We need to find out what version of the operating system is installed on the G5. I believe the first G5 shipped with MacOSX 10.2, later models shipped with 10.4 and they all can be upgraded to 10.5.
Yes, pulling the drive from the G5 is one solution, but I think we need more information before recommending that.