I have a Vista OEM cd. Is it basically worthless if I want to use it to upgrade to WIndows 10?
This is right, I participated in the public beta of Windows 8 on a Windows Vista machine.If memory serves from when I upgraded a few years ago, you can upgrade to Windows 8 from Vista. Then you could upgrade from that to Windows 10 provided there free upgrade still works. They officially ended the free upgrade a couple of years ago, but the last times I've tried it, the free upgrade still seems to work.
Those I think sold for 40 bucks new in 2012. So if that's legit, that's probably about the cheapest legal path from Vista to 10.