Setup each NIC to use DHCP (assuming you have already successfully installed the cards and their drivers, and at minimum the TCP/IP protocol. XP should do all that for you automatically).
Connect each card via regular CAT5 cables to the two router ports, then connect the power and phone cords to the router.
If you ever get broadband, connect the cable/dsl modem into port one on the 56Net, connect a second router with DHCP disabled (as in the cable modem; acts like a transparent "bridge") to port two on the 56Net, and plug your systems/nodes into that second router, with *its* static or assigned IP address (from the 56Net) used at the NICs' gateway. You just don't want two servers (routers) with DHCP services enabled; all need DHCP client enabled, but only one can be a server, which should be the 56Net as setup, since you cannot turn its DHCP server off (another reason I prefer the other router solutions, which do allow me to turn off DHCP services).
Anyway, back to the present:
Setup each to use 10.0.0.2 as the default gateway.
Subnet should default to 255.0.0.0.
Reboot or use WINIPCFG (Win98), IPCONFIG (W2K), or whatever to release/renew your NICs' IP leases. With XP, just try "Repair" after right clicking on the NICs' system tray icons. Leases expire every 24 hours.
Then set your browser to http://10.0.0.2 and logon to the 56Net using "admin" as username and "epicrouter" as password. Setup your dial-up information, submit, save and reboot and you're good to go.
You may need to logon (http://10.0.0.2) each time to explicitly click to "Connect" your modem, although theoretically you can set it up to dial up anytime a TCP call is made (http, ftp, smtp. etc.) from any node on your LAN (I think you're limited to 25 via a 2nd router with the 56Net)... it rarely works.
If yours is like mine, it will need re-set and even power cycled several times per day if you're on more than an hour at a time. You can tell it to auto re-dial when the connection is dropped, but again, that's a crap shoot compared to similar setups with other routers. I'd just leave the quick connect unchecked. If your phone line quality is low (noise is high), you may need to enable the "Failsafe" mode. If you have call waiting, enter "*70" in that box.
Mine has gotten worse with time -- much worse after about 18 months' use. But I was re-setting it even when it was new, which I didn't have to do with similar "broadband" routers (SMC Barricade, DLink 704P) with external serial modems (and also print servers built into those). But those also sometimes did need the explicit "Connect" command from the router webpage when it should have connected automatically...
Sometimes when it stops working but the webpage (http://10.0.0.2) is still responsive I can just click the reboot button to get it functioning again (although that kills the current connection). Other times (like now) it maintains the Internet connection, but the webpage itself is unresponsive, go figure.
Good luck. I think it's a worthwhile purchase for what it does. If yours goes bad though, consider replacing it with an SMC or DLink and a serial external V92.