Perhaps something like this:
#!/bin/sh
cd /path/to/rails
if [ `/usr/bin/whoami` = 'root' ]; then
/bin/su -c "/usr/local/bin/mongrel_rails start -e production -p
6001 -d" rails_user
else
/usr/local/bin/mongrel_rails start -e production -p 6001 -d
fi
