You can run this Micro$oft program to check if a PC will run Windows 7 :- http://www.microsoft.com/en-us/download/details.aspx?id=20
But if both PC's are running poorly I would go for the refurbished PC idea, or maybe a couple of budget laptops.
But if both PC's are running poorly I would go for the refurbished PC idea, or maybe a couple of budget laptops.