how to resign - what to tell my team?

How do I most effectively explain my resignation to my team?   

I recently listened to the podcasts on how to resign.  I got a lot of benefit from them.  It’s just what I expect from MT: simple, clear advice.  The advance preparation of transition documents in particular is fantastic advice.

What was not in that cast was any advice for communicating the decision with my team.  I am struggling to think of something.  I am very close to my group.  I’ve been managing them for several years and together we have really improved things.  I am not leaving due to problems with the company.  I was approached by a recruiter with an offer that is too good to pass up, a great fit for my skills and experience and a step up.  I have enjoyed working here and my departure is going to come as a surprise to everyone.  But I must do what’s best for my family and my career.
 
My group is going to be upset and some will probably feel betrayed.  I’m sure that I will be emotional myself.  I want to explain this as effectively as I can, but I don’t see a way to make it positive for them.  I am not going to a competitor, so I hope I will have the chance to stay on for 4 weeks to assist in an effective transition.  The worst thing would be if the company escorts me directly out the door.
 
My preference would be to tell my team as quickly as I am allowed to by my boss.  I would like to do it on a Friday so that they will have the weekend to process it personally before we continue working together the next week.
 
I would appreciate your input.  The date is coming quickly and I am concerned.
 
Thanks.