[UncleSalty]

Most plans will not allow you to make a withdrawl unless you can prove some sort of hardship. If you do withdraw all or part of it there is a 10% penalty on top of whatever income tax you will pay on the money you withdrew that year. Also, I believe if you make more than one hardship withdrawl in a given period of time you are prohibited for further contributions for a certain length of time. (I'm fuzzy on the exact details there.)

All in all, the government puts some pretty strong incentives not to do this and if you think you'll need the money before you retire you should just lower your contributions, not withdraw from the account. Make sure you are at least contributing enough to get the full company match because that match is a guaranteed instant return on your investment. You always want to be getting 100% of the possible matched funds from your company, it's essentially the same as giving yourself a raise.

Also, if you need the money for some specific purpose and don't plan on pulling money out more than once or twice, some plans will allow you to withdraw up to 50% of the balance as a loan. There will be a small administrative fee and you have to pay the loan back to yourself (with interest,) but you will not incur any taxes on the amount you borrow. Also, if you leave the company you have to pay back the balance of the loan in full so don't do this unless you plan on staying a while. Your 401(k) provider should have all the details on these options, so check their website or give them a call.