If you are changing your W-4 form that you provide to the payroll person on your job - http://www.irs.gov/pub/irs-pdf/fw4.pdf - the filing depends how you are going to file your tax return.
If you will file as "married filing separate" - and will not claim any dependents - you need to check the box - "Single" - see the note on the form - If married, but legally separated, check the “Single” box.
For yourself - you would need to claim two allowances.
Your tax withholding depends on the amount you are paid and how are you paid - weekly/biweekly.
Let me know if you need help with estimations.
If you take a look at the worksheet attached to the form W-4 - you will see, that you should choose one allowance as you are single and one allowance because nobody will claim you as a dependent - total two.
So your normal filing would be Single with two allowances.
However because you are changing withholding in the middle of the year - you might want larger withholding to cover the past time - you may consider to choose zero allowances for 2009 and change it to two starting 2010.
is there a percent of tax taken away from me per allowance removed? if i would change to zero right now how much more tax would be removed from my paycheck this year?
One allowance is associated with additional $3650 taxable income (for 2009) - there is no any predefined percentage.
The actual withholding is based on your wages - the more you are paid - the higher withholding percentage.
Your payroll person is using tables published by the IRS.
If you file zero instead of two allowances - that will give the same result as you have $7300 less in deduction.