If you want to have the module autoloaded on access to /dev/osst, you may
add something like
alias char-major-206 osst
-to your /etc/modules.conf (old name: conf.modules).
+to your /etc/modprobe.conf (before 2.6: modules.conf).
You may find it convenient to create a symbolic link
ln -s nosst0 /dev/tape