|I am afraid you were told right but for completely wrong reasons although dial up is a lot slower than wireless. |
Wireless routers are designed to be used on broadband, that is cable or DSL, which is a completely different technology than 56K dial up.
The only way that it could be made to work is if you could get yourself a dial-up router but they are as about as common has hens teeth and expensive. Even when dial up was the norm, dial-up routers were expensive, even more so now if you can actually find one.
You can still use the wireless router to connect you laptop and the tablet to each other, you don't need the Internet to make a local connection. You would still have to connect to the Internet via the 56K modem.
To do that you will need to make a temporary wired connection to the wireless router in order to configure it. That should be easy is the laptop also has a built in Ethernet connection. Most do these days.
The simplest solution though would be to buy a switch and you can connect your laptop to the tablet with that, that is assuming the table also has an Ethernet connection.
An even simpler solution is to connect the laptop and the tablet directly with a crossover cable which is designed to connect two devices to each other.
Once you have the laptop and tablet communicating with each other, you could set up Internet Connection Sharing on the laptop which would give the tablet access to the Internet via the 56K Modem.