There is in fact now a version of doom that supports client/server based internet play. The source code to the original doom games was released a few years ago now but it's taken this long for someone to come up with a proper c/s implementation. There is, however, some contention about this in the doom community as the author refuses to release the source code in full. The doom source was originally released under its own license which would have allowed this, but has since changed to GPL. Anyway you can judge for yourself at http://csdoom.sourceforge.net.
Slashdot Mirror
There is in fact now a version of doom that supports client/server based internet play. The source code to the original doom games was released a few years ago now but it's taken this long for someone to come up with a proper c/s implementation. There is, however, some contention about this in the doom community as the author refuses to release the source code in full. The doom source was originally released under its own license which would have allowed this, but has since changed to GPL. Anyway you can judge for yourself at http://csdoom.sourceforge.net.