Installation problem: can't find $libdir

Hello,
I've been trying to automate the installation of a PG 7.3.3 database on
a new machine, starting with a tarball containing the 'binaries' for the
system (i.e., everything but PGDATA). (The idea is to avoid
distributing, compiling and cleaning up a full source distro.) I can get
the initdb to work correctly, and the postmaster starts, but my attempt
in install plpgsql into the database fails with:

[root(at)cheviot postgres]# LD_LIBRARY_PATH=/usr/antura/postgres/lib;export
LD_LIBRARY_PATH; su -l antura -c "createlang plpgsql template1"
ERROR: stat failed on file '$libdir/plpgsql': No such file or directory
createlang: language installation failed

Here, antura is the postgres superuser, and (for this example) I've
tried setting LD_LIBRARY_PATH as as shown, even tho' the plpgsql.so
shareable lives in LD_LIBRARY_PATH/postgresql in 7.3.3. I've tried all
combinations of libdir, LIBDIR, and paths, but always get the same
error. The env variable doesn't appear to be set when the language
handler is being created.

Has anyone seen anything like this?
Rich Cullingford
rculling(at)sysd(dot)com