Well it took quite some time to get an X500 Toshiba laptop to connect to a Pioneer PDP-4270XD plasma TV, so in case you are suffering the same issue of no display being output through the HDMI socket you might like me find that the problem was due to an old bios... Updating the BIOS was all that was required to get the system to output to the TV.
Also to avoid vertical refresh issues it appears necessary to "extend the desktop" rather than mirror it to the TV. Not sure why that is the case, might investigate this at a later date.
During my investigation I undated the Nvidia drivers etc. I have noticed that some of my HDMI cables do not work with the X500 laptop, but do work with other devices successfully, so if you are still having problems try another cable as well before you give up.