No one's developed a pigg file reader that's specifically compatible with Win 7/8, but you should be able to get it to run by making a few settings adjustments.
To get it to work with Windows 7, I made these changes on the "Compatibility" tab of the program or shortcut properties:
- Run this program in compatibility mode for Win XP SP 2
- Disable visual themes
- Disable desktop composition
- Disable display scaling on high DPI settings
- Run as an administrator
I don't know what the settings options look like in Win 8, but those would be similar things to look for.
Keep in mind that you still can't use the import feature to update textures, but you can view, export, and get sounds to play.