To enable vsti support in ardour you must compile it from source, this has to do with licensing of the steinberg vst sdk. Here are my basic instructions for doing this on Fedora 10, note that I have already installed the ccrma repository and kernel as well as many packages referenced in my earlier post.
cd ~/Download/ && wget http://releases.ardour.org/ardour-2.7.1.tar.bz2
bunzip2 ardour-2.7.1.tar.bz2 && tar xf ardour-2.7.1.tar && cd ardour-2.7.1
get vst2.3 zip from steinberg, put in ~/Download/ardour-2.7.1/libs/fst
yum install liblrdf-devel libgnomecanvas-devel aubio-devel fftw-devel libsxlt-devel gcc-c++ boost-devel
cd ~/Download/ardour-2.7.1/
scons VST=1
scons install
