Watching the Audi Channel one night the PB screen went black (that was before it stuttering on the internet connection). When...

I wouldn't bother unless you're really attached to it! Copy the files off that you need (including confg settings that you use for other applications) and then transport to a newer MacBook. Or, use the hard drive as an external and port to a new MacBook. Safer in the long-run. Agreed it might be more expensive to try and get it to work with the new OS, but clearly it's not designed to run OSX of the version you want to run. You can get a new/newish one from eBay or visit the Apple website and look at the refurbished section. There you'll find loads of them (depending on stock and availability). Hope this helps.