It could be done.
Easy way is to have the dekstop computer with internal pci 56k modem sharing it's internet connection.
But that computer would always have to be on.
Other way to do it:
Get a external 56k serial modem.
Get a router that have a com port (serial db9).
The SMC7004BR do have that port:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250233151528
As it does not have wifi, you would have to get an accesspoint for it.
(also up for sale)
But you could now have wireless dial-up netzero/aol on a couple of laptops in the house.