How large is your client network for each device type? Based on your other network question it does not sound like a very large network. You really don’t need to have a separate router for each network. You can have a single LAN with a single router routing traffic between subnets. In other words, put the PC’s on 10.1.0.0/16 and the Mac’s on 10.2.0.0/16 and the router would have interface addresses of 10.1.0.1/16 and 10.2.0.1/16. Since the router knows about both subnets, it should be able to route between them as long as there are no restrictive routing policies in place.
However, since you have the restriction of separate DHCP on each network, you will need separate interfaces servicing each network. DHCP is a broadcast protocol. So, there would need to be one switch servicing PC’s (with DHCP server on this network – or the router capable of passing through DHCP requests) that uplinks to the router on one interface and one switch linking all of the Mac’s going to the other router interface. The other option would be configuring a switch with VLAN’s for each subnet and that could get messy and more complex than you may be looking for. However, that may be really the right configuration for your network – just thinking out loud here. Using VLANs at the switch level can also permit you to have a single DHCP server servicing both subnets using DHCP relay.
The Smoothwall Express application can be run on an older PC to perform this task. I’m not sure if the wireless Netgear router you have can be configured with multiple IP addresses on an interface.