dmesg will show some errors regarding DMA - I don't have a copy here unfortunately. I was using the 0.1.9 version of the drivers from ivtv.sourceforge.net. To fix this, I followed the instructions at http://membres.lycos.fr/badzzzz/ - this details using the 0.1.9 driver set, a 'standard' set of patches commonly applied to 0.1.9, and another one-line patch to fix the DMA issue. It also refers to using a custom ivtv framebuffer X driver, which seems to improve things a lot.
There are probably other ways of doing this, and there are other patches linked from http://ivtv.writeme.ch/tiki-index.php?page=PatchesHowTo which seem to cover the DMA issue as well as 2.6 kernel issues.
My modules.conf looks like:
# ivtv modules setup alias char-major-81 videodev alias char-major-81-0 ivtv options ivtv mpg_buffers=90 ivtv_pal=1 tuner=4 # pick ONE of the following two options # 1) s-video output #options saa7127 enable_output=1 output_select=1 pal=1 # 2) composite output options saa7127 enable_output=1 output_select=0 pal=1 options tuner type=28 pal=1# PAL tuner options msp3400 once=1 simple=1 add below ivtv msp3400 saa7115 saa7127 tuner add above ivtv lirc_dev lirc_i2c add above ivtv ivtv-fb
The IVTV TV-out PAL page covers this in more detail