clustalx uses libXm.so.1 
This file is  an XMotif library. In earlier Red Hat
releases, XMotif was supplied by the lesstif package.
Now, a different library is supplied. This brings
two problems:

First, the generic RedHat install has two broken links
in /usr/lib to libXm.so.1 and libXm.so.2. These can
be fixed by adding a link to libXm.so in 
/usr/X11R6/lib.

lrwxrwxrwx    1 root     root           23 Jul  6 12:58 /usr/lib/libXm.so -> /usr/X11R6/lib/libXm.so
lrwxrwxrwx    1 root     root            8 Jul  6 12:50 /usr/lib/libXm.so.1 -> libXm.so
lrwxrwxrwx    1 root     root            8 Jul  6 12:50 /usr/lib/libXm.so.2 -> libXm.so


So far so good, but and now both programs find
the file, but both end up with segmentation
faults

I have also tried installing libXm.so.1 and libXm.so.2
individually, from the lesstif-0.93.91.91-1, which should be
the most recent version.

With these files, the programs run, but again, but the
interface looks a bit different (eg. white space where
there shouldn't be any) and segmentation faults
occur frequently. 

It looks like there is a compatability issue, I'm guessing
with Vibrant.

The fix for clustalx is to include libXm.so.1 in $birch/lib-linux-intel.

If you need further information I'll try to answer your questions.