First off, it is entirely possible to share your internet connection. Earthlink does nothing to prevent this.
Second, Earthlink's policy is that if you do this on your own, you're "on your own". They will not support your networked connection nor help you with a problem related to sharing the connection. If you have a connection problem, Earthlink will ask you to remove the router and connect your DSL modem directly using PPPoE software like WinPoET or Enternet. If for any reason you decided not to remove the router and your case had to be escalated, then it may prolong your resolution by refusing to remove the router.
Finally, do you want Earthlink's help and support with networked PCs?? If so, it will cost you... $7.95 per month... See their webpage here, »www.earthlink.net/highsp ··· working/
, for more information.