Actually, Davis seems to just follow the UC-wide criteria for graduate student residency, which are not that bad. Not nearly as draconian as some schools (e.g. Wisconsin has the "must work here for a year without going to school" rule).
If you live in CA now, you should be considered in-state for the application, because you will have lived here for a year before *matriculation* which is what counts. A few pointers:
1. On VMCAS, claim CA as your state of residence. List your current CA address as your permanent address and do not list any other addresses. (Hopefully it would not be too hard to argue for TX residency despite a CA address at the TX schools if your parents still live there etc.)
2. Get a CA driver license as soon as possible, and if you have a car, register it in CA (these are actually required by law if you are going to be living here more than a month anyway).
3. Register to vote while at the DMV. Oh and by the way, *definitely* get an appointment at the DMV rather than waiting in line!
4. Pay your 2007 taxes as a CA part-year resident listing the date you moved to CA (which should be more than a year before your intended matriculation). Do *not* let your parents claim you as a dependent on their TX taxes.
5. Move your checking account and any cash savings accounts to CA. If you have an internet money market account, IRA, CDs, or any kind of long-term investment, you do not necessarily need to move those to CA banks.
6. Stay in-state through semester or quarter breaks, especially over the holidays. Going home for a couple days is OK, but keep some dated credit card receipts for purchases made in CA within a few days of Thanksgiving and Christmas.
Good luck!