The x-surf is a z2 10 megabit network card, like the ariadne 2 and several other z2 cards which are nowadays not easy to find. (Tho the xsurf is still produced iirc).
It would help if you'd know which modem you'd get. Chances are high that you''ll get an USB cable modem. It would be nicer if it's possible to get an ethernet cable modem, it would allow the connection of a cheap router. This makes it possible to share the same internet connection with a lot of computers.
