edit rules and remove ENABLE_JACK = no from line 48
cd ..
dpkg-buildpackage -rfakeroot -b
then cd back to below your portaudio source directory
install the new debs
sudo dpkg -i libportaudiocpp0_19+svn20071207-0ubuntu1_i386.deb portaudio19-dev_19+svn20071207-0ubuntu1_i386.deb libportaudio2_19+svn20071207-0ubuntu1_i386.deb
then restart mixxx and jack and it should all work
Its the same on hardy.
so to do the fix on both hardy and gutsy :
sudo apt-get source portaudio19
sudo apt-get build-dep portaudio19
cd /portaudio19- 19+svn20071207/ debian
edit rules and remove ENABLE_JACK = no from line 48
cd ..
dpkg-buildpackage -rfakeroot -b
then cd back to below your portaudio source directory
install the new debs 0_19+svn2007120 7-0ubuntu1_ i386.deb portaudio19- dev_19+ svn20071207- 0ubuntu1_ i386.deb libportaudio2_ 19+svn20071207- 0ubuntu1_ i386.deb
sudo dpkg -i libportaudiocpp
then restart mixxx and jack and it should all work
it runs slower than it used to on gutsy for me.