You will need version 1.2.7 (or higher) of the GIMP Toolkit (GLIB/GTK). Also, you might need to install certain development packages, which include header files and scripts necessary to compile XMMS-crossfade. Look for RPMs called libglib1.2-devel and libxmms1-devel.
Then, it's just the usual stuff:
Alternatively, you can install the one of the binary packages (RPM or Debian). If you have a recent release of your linux distribution, it might be included, although it probably will not be the latest release.
You need to restart XMMS before the new plugin is recognized.
Since this has truely been a FAQ, here is some info on the
'xmms-config not found' issue:
'xmms-config' is a small shell script that comes with XMMS. It is
used by plugins to query for compiler flags and installation directories.
When building XMMS from source, it should be automatically
installed together with the
'xmms' binary. On the other hand, if
you installed XMMS as a binary (i.e. RPM or DEB) package,
'xmms-config' may not be included. If this is the case, it is
often contained in a separate development package. Mandrake, for
'xmms-config' in a package called
'libxmms1-devel'. Other distributions may have a different naming
scheme. Start looking for a
'*-devel' package, or use your
distribution's package management tool to search for the package
Note that what I said about
'xmms-config' above also applies to
'gtk-config'. If the configure script complains
about missing GLIB or GTK, you probably have to install the
respective development packages.