This requires qt 3 or later.  See http://www.trolltech.com

To support the widgets needed for this code you need Qwt:

http://n4hy.org/Qwt/qwt.spec
http://n4hy.org/Qwt/qwt.pc
http://n4hy.org/Qwt/qwt-5.0.0.tar.bz2
http://n4hy.org/Qwt/qwt-5.0.0-1.src.rpm

QTDIR is an environment variable that must be set for
gr-qtgui to make.

On Ubuntu with a standard apt-get or synaptic install,
this is done by:

export QTDIR=/usr/share/qt3

on Fedora Core 6 for example it is automatically set to 

/usr/lib/qt-3.3

by Qt install

Qwt probably needs to be built and installed for now using

rpmbuild --rebuild qwt-5.0.0-1.src.rpm

which must be run as root (as in sudo) so that files are
installed in the proper place for the gnuradio build
(such as qwt.pc).