You can buy Windows 7, no it's not free, but can be found quite cheap. If you'd bought an upgrade from XP to 7, no you couldn't go back to XP, but you could if you'd bought a retail version of 7, you would also have been able to move that retail version to new hardware free of charge. I don't think you can activate XP now, but I suppose if you imaged your XP installation you would not have to worry about that. If you have a spare hard drive you could install 7 FOC for 30 days before having activate it, and see how it goes.
With Apple you pay a vast premium in the first place, so don't get me going on Apple, they beat manufactures down to the bare minimum price and charge end users the absolute maximum, which unfortunately has led to the likes of MS doing the same with hardware, as is Samsung. The only thing I ever wished I'd bought of Apples was their shares a long time ago.
Linux is well Linux, and like you say free, can't beat that so why did those hardware manufactures not use Linux for their scanners???
Anyway I'm off to bed.