Message #70370

[Atlanta Z3]

Been there.  Not giving the extra week can burn a bridge you might not want to burn.  However the new company wants you to start.  A couple of options, first I would make a call to your new manager and explain the situation (if you are thinking about staying), and feel them out.  If I got any push back on the start date that would be my decision.  Cut ties and move on, because that is where your future is. 
Another option I have offered is after hours or weekend training for the replacement- and not for free, either still on payroll or consulting paid.  I have also left a forwarding email, that if it is critical I will check at lunch and respond as possible.  Here again don't jepordize the new job by hanging on to the old job.
When I had this situation it actually worked to my advantage because the new boss was going to be on vacation that week, but they had me starting early to work with other departments as filler work...
One final note - a three week notice can be painful.  If every one in the office knows you are leaving and they start to give you grief or all the crummy assignments no one else wants - or just the guilt trips.