There are a number of 401k type plans. Different ones allow different things.
There is a new Roth 401k that if you have can do what your asking well.
http://www.irs.gov/retirement/participant/article/0,,id=151753,00.html
Roth 401 (k) plan
Roth 401 (k) plan
Roth 401 (k) plan
How much tax do I have to pay on 1,000 dollars
No.
That depends on how much the tax is.
im a single mum self employed. how much tax should i put away out of 700 a week
A 401(k) is a retirement savings plan that allows an employee to contribute a portion of his cash wages to the plan on a pre-tax basis. These deferred wages are not subject to tax withholding.Click here to fill out the 401(k) Tax Benefitsform
That depends what the level of tax is.
An 8 percent sales tax on 26000 dollars is $2080.
$87.99 dollars (Without tax)
The tax is $1.86