is it still possible to use a sega saturn netlink?

You can't hook Ethernet up to a modem, but you can still use the modem via a dial-up ISP to play some DC Internet games, like Quake III. IIRC only a few online games on the DC support the broadband adapter tho.

 

You can get software that will run a dialup server on your PC. You connect the PC's modem to the console using a telephone cable and the PC fakes the line signals, and then passes it on through your normal broadband connection. We used to do that with PSO on the European DC version because AOL would not work on it.

This webpage outlines the method with a DC to PC. I am guessing it would work of the Saturn and N64DD too: http://dreamcast.onlineconsoles.com/phpBB2/guides_pcdcwin98.php