But if I live in a house with 2-3 other PS3 users, will it be possible to play online together? i.e. can I open ports to more than one PS3? All this ports business never used to be a problem when I lived with 3 other SOCOM online players. It only became a problem in later games for some reason.

Anyway, it will be a long time before all 4 of us have PS3s. We all want one, but aren't in a hurry until the rumble is fixed, and of course until MGS4 is released...