My 16 yr. old just started working as a busboy at a restaurant.he is fiiling out his w-4 form.what I want to know is does he put a number of dependents on this form or does he put 0 on it.

The W4 has to be filled out.

If he elects to select 0 Dependants (zero), he will get more money back when he files his 2008 return. This also means that they will take a litte more from his pay checks.

If he selects 1 dependent, they take less money from his check and he gets less money back when he files his return.

He should put 0 or 1 allowances on your W4. The purpose of W4 is to guide your employer how much tax they should withhold.
If you put more allowances on your W4, your employer will withhold less federal and state taxes from your pay check. Then you may owe taxes when you file your tax return.

Read: Your U.S. Tax Return: Filing W4 Employee's Withholding Allowance Certificate

If he is single and YOU are going to claim him as a dependent, he should definitely claim NO MORE than 1 exemption on his W-4. This will ensure enough money is withheld to cover his tax liability.