<<< have second pc with either windows 98se or me this connects to internet via dial-up-connection
this pc has nic card fitted and in device manager is working ok/also a cat5 cable connected to same >>>
What is the CAT5 cable connected to? It should be plugged into a second LAN port in the router and, if this is the case, it should already have internet access via the broadband connection. There is nothing more to it than that.
<<< also if possible connect a 3rd pc in the future as above(wins 95/98/me0 >>>
As long as it has a network adapter installed, plug it into a free LAN port in the router too.