Hi I just got scammed buying a laptop and I'm next to hopeless when it comes to this sort of stuff, so I guess I'm off to a shaky start... ;-O.

It's running a dodgy copy of Windows 7 with loads of software and programs I don't even understand. Regardless, I've managed to tame the annoying popups and ad material down to a manageable state. However, when I'm using Google Chrome these hideously irritating popups for something called 'Supra Savings' keep coming up, making it almost impossible to negotiate the screen. I've tried going to Uninstall Programs to get rid of it, but nothing exists under Supra Savings! Help!

From Programs and Features uninstall anything you don't need. Then download and run this excellent utility: Malwarebytes | Thank you for download Malwarebytes Anti-Malware
Quarantine anything it finds.

Yes but how do I know which program it's installed with?

You don't really need to know that.
Another weapon is to install Ccleaner and use its Startup feature: Piriform - Managing auto-starting programs
Make sure to select the tabs for the browsers:
Attachment 46040

Does the laptop have a CoA (Certificate of Authenticity) sticker on it. If so it should have the Windows Product Key on it, and you can just wipe and re-install Windows and start from scratch. That's if you don't mind losing the current information on it. Since you just purchased the laptop I doubt you need all the crap the previous user had on it.