is not avalible in a DIP package option
.. and never will. However there are break-out boards, but in most cases they are not strictly Dual In Line but either quadratic (as the chip), or Quad In Line so to speak..
The power of the Mega128 (not only the number of pins, but the 4 UARTS and the RAM) will come in handy for many real-world projects.
But you also will have limited support.. shields and libraries will sometimes not be compatible ... know-how in this forum is more limited....