When you close out yout 401(k), they will probably withhold some tax. It usually isn't enough. The distribution is reported to you on a form 1099-R and you enter that on your tax return to calculate the correct taxes.

Since I don't have any information about the rest of your income, I'll give you some rough numbers: assume about 15% income tax, 10% penalty if you're under age 55, plus your state tax income tax (mine is about 7%) -- so you're looking at 22% (around a thousand of your four) going to taxes. Your actual numbers will vary, you might want to carry your info to a tax preparer who can give you a better estimate.

It is a lot cheaper tax-wise to roll the money into an IRA -- no tax consequences for this action.

If you are not longer with the employer, and your balance is under $5000 they will usually make you move the account. Within a few months they will notify you if this is the case. The notice will give you 90 days to decide or they will automatically roll to an IRA of their choice.. (problem here is there is a distribution fee every time you move the money)
If you cash out a 401(k) they must withhold 20% automatically (more if you ask) so $4000 - 800 for federal tax, plus any distribution fee, and any mandatory state taxes... as reader states,... you may owe more when you file your taxes, and the 10% penalty will have to be paid as well. (if it applies)
So in answer to your question, depending on your state you are likely to received... around 3100-3200 in hand, and still have to pay the penalty and any additional taxes... aside from the mandatory 20%----

Thanks!