windows7 upgrade from beta

Hi all,
I have tried to upgrade to widnows7 full from the beta but get a windows error - 'product code unattended answers file' - on clicking ok, windows reboots then tries to install again with the same error - ad infinitum.

I have even gone as far as uninstall/reinstalling parallels but for some reason the fact i have a windows installed previously is remembered and the old bate product code is casueing the mis-match once again.

is there a known solution to this?
failing that...
Is there anyway I can manually edit the unattended answers file? (i think it's an xml/txt file)
failing that...
Is there anyway I can completely destroy any hint of there ever being a windows installed?
failling that...
why don't ms have decent support? - (this one I don't really expect an answer too).

any hints of tips to solving this would be hugely appreciated.