Note on jack and real-time audio.

You will profit from a kernel with the realtime patch set applied. Slackware's
kernel does not have a realtime kernel, you will have to compile it.

You still can profit when jackd runs with realtime privileges.
One way to do this on Slackware would be to use set_rlimits (not part of
Slackware). Since 12.2 there's another way, though experimental.
If you have a filesystem that supports posix capabilities (reiserfs does not),
you can grant jackd the rights to run in realtime mode, even when started as
normal user with the following command:

  # setcap cap_ipc_lock,cap_sys_nice=ep /usr/bin/jackd

The post-install script of the jack package runs this exact command,
so that you do not have to.