Due to a mass of trolling, only established posters are able to post in non-newbie sections. You are considered "established" if you have spent 4 hours online and have made 5 posts (new topics or replies).
If you have really good posts, you can post a request for preemptive whitelisting in the appropriate topic.
Also: - Newbies cannot upload their own avatars. - You must have made one post in order to send PMs. - You need 10 posts to put a link in your signature.
Note that it may take up to 10 minutes for your PM or posting permissions to be granted. (The system automatically checks every 10 minutes and promotes people as appropriate.)