Due to past problems with spammers, there is a post limit before you are allowed to do those things. Once you hit 10-20 posts, I think it is, you should have no problem.
I think it's also 100 posts before you can edit your posts. (Or did that change?)
That is correct. The reason for it needing 100 posts is because we were getting spammers who would make 20 or so posts, let them sit so they fell off the radar, then go back and modify them all to add spam links.