OK, the following seems to work fine, both on my home system and at my client's.
- The regular router and the wireless router were both by default using 192.168.1.1 as the local address, with a conflict. I used the browser admin interface on the wireless router to change its settings to 192.168.1.205 (arbitrary number 205, anything greater than 1 through 10 and less than 255 should work and not interfere with the DHCP addresses handed out to attaching PCs on the LAN).
- I connected from the UPLINK port on the wireless router to a port I made available on the regular router. (All the ports on the regular router were in use, so I moved a PC from the regular router, used its port for the wireless router, and plugged the PC into port 2 on the wireless router).
- This worked, all the existing PCs still had Internet broadband (cable modem) access, and so now did wireless clients. The WAN port on the wireless router is unused and thus inactive and doesn't seem to be an issue.