I recently felt brave and decided to install Toshiba's Satellite P100 BIOS v4.2 (released 11/21/2007). According to the release notes they added "64-bit OS support". Now I can finally use the 4GB of memory I have installed.
The memory may have shown up in earlier BIOS releases...I skipped 3.8 and 4.0.
Anyway, I have attached the original v4.2 DSDT source and my modified version. Makes sound, acpi, nvidia fan, etc. work "properly".
-Justin P. Linenkohl