Using linux means stuff doesn't always just work by itself, sometimes you have to fix it. Google is your friend. Search for "linux kernel VIA Rhine II Fast Ethernet Adaptor". My kernel says it has support for VIA Rhine cards. You might have to compile support for it into your kernel yourself. Something you would've done anyways had you used Gentoo, as part of the install process. forums.gentoo.org is also your friend. *wanders off*

PS: Yes I do, point being?