I'm loged in with facebook open id. I can post questions and answers. I can edit my profile and I see my login name and reputation point at the top of the page. But when I try to vote I get "Please login or register to vote for this post." message.
Not only do you need more reputation, but you also don't have a registered account (with askubuntu--I see you have a registered account with SO). Even if you acquired enough rep, you'd still need to register (to vote). It is explained in the FAQ (regarding registration) and this part of FAQ (regarding reputation and what you can do with your rep points).
If you do decide to register, you only need 15 points to up-vote. (It is explained here.)
You should make sure that it is not because of insufficient reputation. You need 15 reputation to vote, and you get rep when someone upvotes your question or answer. Go and answer some questions, get some upvotes, then you should be able to up and down-vote for yourself.
Your username at the top of the page is updated dynamically, whilst the rest of the page is not. You are looking at a cached version of the page. You need to refresh the page (F5) in order to be able to vote.
However, voting up requires 15 reputation and voting down requires 125. You don't have sufficient reputation to be able to cast votes. Refreshing the page will remove the "please login" message, but you will have to earn more reputation in order to be able to vote.