dead reck for ifr??????
well i dont think you can fly DR on a IMC flight.
you fly to the fix (in this case the IAF) in 3 ways direct following the navaid (VOR, NDB whatever), radar vectored or following a STAR.
for example the last post contained a VOR approach, so you fly to the VOR as per filed or with the altitude given by the controller then when you are intercepting the IAF you are in the published portion of the IAP and you can start descending as per proc.