Can you use an ADSL router for dial up connection?

Don't use a cable modem for dial up. Use the modem in your computer or an external voice/fax modem for dial up. If you want to share the internet connection with other computers use Internet Connection Sharing (ICS) in Windows. Search Windows in Information in Help and Support Center for the Internet Connection Sharing setup in Windows XP. To use ICS you will have to logically connect all of the devices into one network. Hopefully all of your computers will self assign an IP address that will let them talk to each other then all you need are network cables and a switch. You can also use the swith (LAN) portion of your cable modem as a router to assign IP addresses (DHCP) to the other computers to ensure the other computers are on the same network.