Normally PyQt4 is not needed during compiling, it's just used at runtime. For some reason it seems it is not correctly installed on your system... Does it work when you do this, in an external python console:

import PyQt4
from PyQt4 import QtGui

If it works, then it should work in FreeCAD too, check that the python version in the FreeCAD python console matches the python version in your external python

If not, then something is not correctly installed... What distribution are you using?