[LAU] Xruns and Thinkpad T60

Hi Everyone, I'm struggling to transform a Thinkpad T60 into a decent audio system. I've installed ubuntu studio Feisty and a realtime kernel from texware.it. When I run jack in realtime mode using for example 512 frames/period, it shows in its messages a lot (>10/sec) late driver wakeup warnings and does a lot of xruns (>1/sec). I've changed the IRQ priority of the sound card (an HDA intel) to realtime but this does not change the warnings/xruns. It's not the first time I setup a computer for audio and so far succeded using 64 frames/period. Here I tried every settings I could (periods/buffer, samplerate, even tried with a Maudio Fast track pro) but still no joy. This Thinkpad has an ATI graphic card (not on the same IRQ as the sound card) and uses fglrx driver. Could this be the culprit? Is there another (free) driver I could use? Does anyone have an idea of what to try next? Many thanks -- Raphaël Bollen.