Is it not just going into your windower > scripts folder, clicking the init.txt and putting the line:
bind sysrq screenshot png hide
That makes my printscreen button take a screeenshot... I mean if I used Windower, of course.
In the past it was a joke, but nowdays there is a long standing glitch in windower that when you boot up an instance of FFXI the screenshot button says it takes a SS but it really doesn't. There has been almost 0 effort to fix it on anything part, so its just one of those things we've all lived with and just use our phones or other programs like snippet.