Yes, there is a penalty for withdrawing from a 401K account early. my father had to pull out a lot from his 401K last year because after he left wal-mart he was making 25K less than he was. he had to pay over 6K to federal for pulling out some his money from his 401K before he was technically "supposed" to.
and he's going to get another fine next year because he's pulling the 6K from his 401K to pay for his taxes.
i suggest not doing it unless it is absolutely necessary.

20% tax will apply. If you are under 59 1/2 (generally there are other exceptions) an additional 10% early withdrawal penalty applies. No matter the reason the taxes will always apply.. the penalty can be waived if you area permanently disabled.. but a second home is not a reason to waive..
20% will be taken out when you get the distribtuion from a 401(k)... the penalty will be paid when you file your taxes next year, (unless you ask the administrator to take it out now)