I checked around the web, and it appears that Sound Forge 8 doesn't support Vista.
You can try to run it in Compatibility mode: Right click the program icon and select 'Properties' at the bottom. Select the 'Compatibility' tab, check the box and use the drop down to choose which mode.
If that doesn't work, then the Vista compatible version hs available here:
Sony Creative Software - Sound Forge 9 - System Requirements