I think it might have had something to do with the scaled down leveling thing, but I got my PBE account yesterday. I was able to login to the client with it, but not the commputy.pbe.leagueoflegends.com site.
Anyhow I'm sure it's just a part of the system that causes the delay between PBE access and PBE community access, but it took almost 24 hours before I was able to post here. If that's not intended/known then hopefully it can be fixed.
Note: I figure it might have something to do with the scaled down level thing since once I was leveled up to 30 and given my starter RP/IP i was also then able to post.