Did you consider building your own kernel? I'm using self-built RT
kernels on Ubuntu 12.04 and that works great:
http://wiki.linuxaudio.org/wiki/system_configuration#build_your_own_real-time_kernel
And are you using rtirq?
Alessio Abogani stopped maintaining th RT kernels for Ubuntu quite a
while ago. You might want to ask falkTX about the possibilities of
offering a raring RT kernel.

Best,

Jeremy

Hey Jeremy!

Yes, that's the other thing I will try now, good to know it works on 12.04.

My pain in the a... is that I have to use nvidia drivers, and had troubles some time ago with them and rt-kernels.

Do you happen to know whether I need to patch nvidia support into the rt-kernel I build? (I guess so... just to be sure)

thanks!

best,
M