What Version Of Windows ????

Hi ! I bought two photo editing programs ( Dynamic auto Paint ) which are exe. files ( my mistake )
I have 10.10.1 on my desktop computer...... I am willing to buy Parallels desktop so that can install & use the new programs....... but I also need a windows OS ...... naturally I want to spend as little as posible on the windows version ..... I saw on eBay windows 7 ( $ 40 )... and also windows for mac ($ 80 ) .........
which is the correct version to buy ?????????
also ..... irrespective of the cost ........ any other version of windows that I should consider ???? I do not see any need to use windows in the future other than for this specific editing program.
thanks for your help & advise
No idea, but you may want to look into 'GIMP' or 'Picasa' which are free. 'iPhoto' which is on your Mac, or check out 'Pixelmator' &/or 'GraphicConverter' which are low cost. My choices are GIMP & Pixelmator.

I wouldn't install Windows on a bet!