Hey buddy
I installed Windows 7 of an Tecra A9 Laptop and everything works fine except the sound.
You don’t need the BIOS update because this will not solve the sound issue.
I think you’ve got the same issue like described here:
http://aps2.toshiba-tro.de/kb0/TSB7C021B0001R01.htm
I read in the forum that the same can happen with Win 7!
So check the tool attached to this document and check if this will help you!