Macintosh PC on Windows Network

Hello,
I am trying to add a G5 to a windows base network. My diagram looks something like this:

I am using a standard DSL router connected flat off of my ISP from there I have a Wireless switch, and a normal switch connected off it. I am using half my IP range for DHCP and the other for static, my wireless uses the static the standard switch DHCP. (Security purposes for the wireless network).

Currently I have had a user show up with this G5 Mac. I can get it connected via the switch with a DHCP address using PPPoE protocols and it will connect to the internet just fine. The problem is it wont see anything else on the network. A few years back we had this problem and I was able to make it work with Virtual PC on the mac. For some reason now it doesnt want to work.

What confuses me is that it connects to the internet via the same network, but it wont map to or see anything on the network.

Any ideas?

They can't see any servers or network printers? Can you browse to the servers or network rinters by IP address?

I'm pretty sure Macs don't support Windows networking out of the box. I would expect that you can ping the other machines OK and you can use all the standard protocols like TCP/IP.