I have a dell latitude d510 currently running xubuntu 13.04 and linux 3.8. I want this machine to host JACK processes together with EDIROL UA-25 during a live session and therefore, it needs an RT kernel. Since this is a laptop, I do like to have no RT kernel installed also saving power. How can I configure this?
The easiest way would be using a lowlatency kernel, which you could do by installing the appropriate meta package linux-image-lowlatency, respectively linux-image-lowlatency-pae for 32 bit systems.
With different kernels installed, grub will allow you to choose between the available kernels when booting. So you could use the lowlatency kernel for music sessions and a 'normal' one for power savings.
I recommend using the lowlatency kernel instead of a realtime kernel because there currently are no official packages for the latter – as per this question here on AskUbuntu – and thus even the Ubuntu Studio guys recommend trying the lowlatency kernel first.