Network Topograpy to allow three seperate networks share one network printer

Just need another router and create static routes to the printer.

Let me see if I understand.  Add anther WRT54G and add static routes between routers from each of the other WRT54G routers (ie 192.168.31.1-*.33.1 to the new router IP address?)

I don't think that WRT54G will work as a router. you need 3 ports belonging to different networks (VLANs). I think it can only route between WAN port and a switching part of device

Problem is that you need to be able to give the MFP a gateway that will allow a return path to 3 networks. Most MFPs only support one gateway.
You need more than a simple wireless router, unless you want to route all traffic via the WAN ports, which would mean giving the MFP its own external IP and routing via your ISP.
One solution would be to set up a PC with 3 wifi cards and Linux router distro. to bridge the networks via static routes, and connect the MFP to this.(actually, some versions of the WRT54G run Linux, and can be hacked to change their functions, but I cannot recommend this).
Otherwise, you need a proprietary solution.

Another thought, the WRT54Gs have 4 port ethernet switches, you could connect them via the ethernet ports to a pc with 4 ethernet cards, and link the MFP to the 4th card on a different subnet, then set up routing between the cards.
http://www.linux.com/base/ldp/howto/Bridge+Firewall.html

You could also use the network bridge feature of Windows XP, but I have no experience of this myself.
http://technet2.microsoft.com/windowsserver/en/library/8c6c4acb-49db-4d8a-844f-1fe31c4b2ded1033.mspx?mfr=true

It depends really on how much interaction you want to allow between the networks

The only interaction we really want is to share the print device.  I'll take a look the above articles, thank you for your input thus far!

What about this idea:

Setup a windows xp box to act as the print server.  Assign multiple static IP's to the internal NIC in TCP/IP settings, including the gateways.  Then configure static routes in the routing table of the XP machine for the other networks.  At this point I'd have to turn off DHCP and set each workgroup up with static addressing but I think this might work...  Thoughts?

What are you recomendations on brand of layer 3 switches?

you don't need the best of the class switch. All you need is the ability to create and route between half a dozen VLANs.

http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=L3+switch&category0=

I've ordered the Netgear FSM7328S 24 port 10/100 L3 Managed Switch 24 port 10/100 switch with 4 -1Gb ports.  I'll post back as soon as it arrives.

avilov, nice answer.

Just never thought of it, mainly because I don't have much experience of managed switches, our network is only just coming to the point where we need them (and the price has dropped to the point where I can justify it). :-)