the property handler download will enable the flac files you have to show albumart on the file in windows explorer and it will show the tag information at the bottom of the explorer window enabling you to change it as you can already with mp3s, use it you will see the difference,
as for changing the wmp x64 to x86, try this
go to a mps3 file and right click it ,select open with and then choose default program select wmp ( its possible there will be two showing x64 and x86) ,it should be the x86 ,however you could browse to it ,it can be found in c: program files x86 /windows media player . then select the wmp .exe
or try start menu / default programs / in the window that opens select wmp and set as default program.
sorry for not posting sooner, hectic xmas stuff going on with 4 kids.