Glad to be of help, but I recall the Ardour site itself has a page dedicated to information on VST but can't find it atm (it's not www.ardour.org/vst) =/
SDK: http://www.steinberg.net/331+M52087573ab0.html
Download 2.3, most hosts have yet to support 2.4 completely (although Jost does), let alone the new v3. Then you can build:
scons VST=1
scons install
I'm somehow sure that you'll face problems due to gcc or libsnd issues, but you can approach the IRC channel #ardour at freenode network and/or the forums for that. Good luck und enjoy.