To get your tax ID in Texas go to:
http://www.window.state.tx.us/taxpermit/
That link will have you fill out a bunch of info, then print out the sheet it tells you to, sign it and fax it in. In a few weeks you will get your Texas Sales and use Tax Permit.
If you do the above, you’re going to need a DBA (doing business as) if you are starting a sole proprietorship. If you don’t know what that is look it up on google. To do this you can go to your county clerks office and get an "Assumed Name Records Certificate of Ownership for Unincorporated Business or Profession". You also need to research and make sure nobody else has registered the name you want to use in the context of your business. If your not comfortable with doing it yourself there are many online places that will do it for a fee. Legalpcu.com will do it for 35 bucks or so plus the 15 dollar state charge (not sure if I am allowed to post that site or not, if not let me know the protocol and I wont in the future).
Hope that helps,
-Tim