Ok, so the scenario is this:
I have a G5 Quad (running Leopard) with no wireless card.
The G5 is connected by ethernet to a Mac-Mini (running Lion), which is picking up my AirPort Extreme network over WiFi. The Mac-Mini shares it's internet connection over ethernet to the G5 enabling it to connect to the internet perfectly. I can also screen share or ssh into the G5 from the Mac-Mini without any problems.
Now comes the trouble:
I have a MacBook Pro (running Lion) which also connects to the same WiFi network as the Mac-Mini. I can see (and connect to) the Mac-Mini from the MBP without trouble, but I cannot see or connect to the G5 from the MBP. How can I configure this so that I can ssh or screen share the G5 from my MBP?
IPs and subnets of machines:
Mac-Mini
IP: 10.0.0.9
Subnet Mask: 255.255.255.0
MBP
IP: 10.0.0.4
Subnet Mask: 255.255.255.0
G5
IP: 192.168.2.3
Subnet Mask: 255.255.255.0
Best Answer
This is happening because the two machines are not on the same subnet.
The G5 is on the Mac Mini's subnet, while the Mac Mini is on your Wi-Fi's subnet. The IP address of the G5 has been handed out by the Internet Sharing DHCP service on your Mac Mini, while the Mac Mini's IP address has been handed out by the DHCP service on your router.
Your best bet would be to connect your G5 via Ethernet to your router.
If that is not possible because of location constraints, there is a piece of software for Mac called IPNetRouterX that may do the job. It allows Ethernet bridging, which is what you want. The only problem with this software is that it costs money. It seems like there might be a free trial of it, however.