These are the instructions to build the XMP plug-in for Audacious, using the source code from git (not using a release package).
This is for Arch Linux. I decided not to use the AUR package because it failed due to other dependencies and I just wanted to build the plug-in for Audacious, after all.
So these are the instructions:
git clone git://xmp.git.sourceforge.net/gitroot/xmp/xmp
Since we're downloading from source there's no 'configure' file as mentioned in the INSTALL file. We need to run autoconf first, so that it generates the required configure file.
This takes the instructions in autoconf.in and makes a configure file. So we've got the configure file, we need to use it!
./configure --enable-audacious-plugin --prefix=/usr
The prefix is for keeping it compatible with the Arch Linux layout. You can enable more stuff if you want/need, such as pulseaudio, or other plug-ins as xmms.
And as root (or with sudo):
If you had audacious open, close it, and you should be able to open tracker files with Audacious now. Even "open with..." in Nautilus works "automagically" :-)