If I am 59 1/2 and want to withdraw a one-time, lump sum portion of my 401K can I do that? I don't want to start receiving regular distributions yet - just want to withdraw a portion of my account.

Taking a single one-time withdrawal shouldn't be a problem. Something to think about: instead of taking a single lump sum now, you might want to think about taking only part of it now and waiting till early January for the rest, so that you split the lump sum across two tax years - this may avoid pushing you into a higher tax bracket this year.