ubuntu displayed on TV via HMDI (overscan/underscan problem)

[el_oso]

basically hook my laptop upto the TV via HDMI to watch films and stuff via HMDI cable. The output on the TV is not correct. even though it is displaying in 1080p format i either get a problem with overscan using to default drivers for ubuntu or underscan (black borders) with the proprietary drivers. anyone have any ideas in how to fix this. i know that for windows the ATi Catalyst Control centre has a slider to correct for overscan/underscan and that works fine. looking for a solution for my linux OS so that i can hook up my mates (mac format) hard drive without the need to use another hard drive to copy the file across so that window can read it.
a few specs if it helps
panasonic 42" viera
linux mint 9/ubuntu 10.4LTS
intel core 2 duo 2.0Ghz
ATI mobility raedon 3400 series

edit: have a partial solution now. i can play the video fine through HDMI and the scaling is correct but only when the laptop screen is disabled. when extended desktop mode is enabled the overscan/underscan re-occurs. not a huge problem i suppose, just means i can't really use my laptop while watching a film.
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