Limiting their posts only to Beginners & Help can be an option and maybe the only one close to valid.
Stopping them completely from posting should not be done. Asking for some extras (invites) is also bad idea.

Keep in mind that some (few?) newbies are honest and come here with problems or simply for the reason this forum was created (discuss), not necessarily to spam and do bounties. Those should be allowed ask their questions and get the chance to properly describe their problems (which usually comes as a later post), or simply to chat a little.

And yes, that quote from Theymos about newbie jail is very eloquent.