You may need to fiddle with your LD_LIBRARY_PATH or ldconfig. I have
more detail on how I got rmagick and imagemagick working under debian
linux posted here:
Without more error information it's tough to say what might be going
on. There has to be an error showing up somewhere -- are you running
with script/server via WeBRICK in development mode and looking at the
WeBRICK output and your development.log?