You cannot borrow against a 401K. You can take a distribution and pay no tax or penalty as long as you put it back within 60 days. If you do this and it's not back in the account in 60 days you will pay taxes and penalties on the money. Now what you really want to do is get the publication involving 401k distributions from the IRS. This will explain circumstances under which you can take a qualified distribution and pay no penalties.