Some general and useful hints:
==> Install up-to-date kernel (2.6.38.1) or the last rt-patch (still 2.6.33)
==> Install up-to-date JACK (jack1 or jack2, try both and see -- jack2 has support for multi-core)
==> Edit the /etc/security/limits.conf to allow you (user) to have rt priviledges
@audio soft cpu unlimited @audio - rtprio 100 @audio - memlock unlimited
And add yourself to the audio group.
==> Use this script to help you check other realtime related configurations:
http://code.google.com/p/realtimeconfigquickscan/
Hope that helps!