There seems to be a conflict between Windows 2000 using DirectX 9.0b or Windows XP running service pack 2, and Petz 5.
There is a file that gets installed into the Petz folder called 'setupapi.dll' that appears to be causing a conflict with other newer system files installed with the latest Windows service packs.
The workaround is to delete this file (setupapi.dll) from the main Petz folder and try running the game again.
There is a second file that MUST Be deleted in order for the sound to work again. The file is called smapi.dll. Delete these two files and empty your recycling bin. Then Run Petz 5 again. Your Sound should work