(1) The right thing to do is vote for Bill White. Please, please don't vote for Rick Perry.
(2) If you want to know your rights as a voter in Texas, look them up here.
Tomorrow is the last day for early voting in Texas. Even if you are unable to make it to the county in which you are registered (I can think of two people who fit the bill), you can vote early on a limited ballot (It might be good to bring some paperwork to show the people working at the polling station. You can find polling stations here.)
Anon sent an unrelated but not un-fantastic little clip (see comments).
Also, if you want to cast a limited ballot in Texas, know that this is limited to certain polling stations. UTSA, for example, has a satellite polling station and will not distribute the limited ballots to those who are registered to vote in other counties. I checked and this is totally kosher. Probably a good idea to check before you head to a polling station to see if you can cast a limited ballot from there. Haven't found a good resource for this as the sites I've seen do not say that you can only cast the limited ballot from some stations.