Hello there, If you are both working, the worst thing that you can do is both change your status to married on your W4's. Married status causes less tax to be taken out, and unless you have a lot of deductions you will wind up owing.
In order to assist you better, if you can tell me what both of your incomes are for the year and what type of deductions you have, (and how much of a refund you desire) then I can help you plan your W4 exemptions.
One point...Just because you get a larger refund does not mean that you are getting more money, it just means that you had more money taken out during the year. The tax return is a reconciliation of your tax on your income, and how much was taken out--which will yield either a balance due or refund.
Since you live in a community prop. state, you are most likely going to see the most benefit from filing jointly instead of separately.
Your estimated tax liability for 2008 is approx. $8500.
You would need this much to be withheld during the year to "break even" (no refund, no balance due).
If you and your husband both have single, 2 on your W4's, then you will have 9900 taken out, and this will yield and approx. refund of $1400.
ON your pay, you will see 160 taken out for federal withholding if you are paid weekly, and 320 if you are paid biweekly. He will see 31 taken out weekly and 62 taken out biweekly.
To get a larger refund, you can change to single 1 or single 0.
Please let me know if you need more information.