I'm running 3 Rio Receivers in an almost identical situation. My PC is running Win2k. It's plugged in to the same Netgear FS108 switch as two of the Receivers. They both work.
I think that you can discount the router, unless it's involved in the DHCP configuration.
These are general trouble-shooting steps -- I know that you've probably tried most of them already, but someone else might find them useful, too.
The first trouble-shooting step is to find out if you're getting link at the Receiver when in this configuration:
1. Plug in the network cable.
2. Plug in the power cable.
3. Wait 5 seconds.
4. Hit the power switch. Watch the link/activity lights on the back.
5. The activity light should come on solid for about half a second, followed by the link light. They should remain solid for a while, as the Receiver loads its firmware over NFS.
If this is not working, then you've got a cabling problem, or the Receiver's network port is hosed. Now, you know it's not the Receiver -- it works with the other PCs.
The next step is to diagnose your DHCP problems. When the Receiver fails to boot, it will display the networking information.
This is formatted as:
info net:pna ip:169.254.238.208
n:255.255.0.0 g:255.255.255.255
If you've got link in the previous step, you should get "net:eth". If you're trying PNA, then you'd expect "net:pna". The "ip:", "n:" and "g:" sections tells you what IP information was assigned by your DHCP server. If the "ip:" section starts with 169.254, then the Receiver couldn't find a DHCP server and used UPnP to make up an IP address.
Now, some questions:
1. Is your router doing the DHCP assignment, or are you using the built-in DHCP server in the Receiver software?
2. Are the Win2k/98/ME machines configured to use DHCP or static?
3. Does the router do NAT -- i.e. is it assigning private IP addresses to your machines, or is it assigning them from a pool assigned by your cable modem provider?
4. In the Audio Receiver Manager, go to Tools|IP Configuration. Which network adapters are listed in there? Is "Enable Autoconfiguration" checked for the network adapter? If it is, what IP addresses are in the boxes? Are these what you'd expect for your network?
5. Is the "Make Music available" box checked?
More questions as I think of them.