protip, dont use kies, its very buggy and kind of shitty ^ ^
plug in usb, select mass storage, roll down statusbar, click usb, select "mount"
Go to your filemanager on your pc, (winkey+E) find your folder with flac. Right click on folder, select copy. (ctrl+c) Find your external memorycard (x:\) probably e,f or g:
(Also, you can make a music folder on ur card just to be organized)
example x:\music\FLAC\ )
Then paste , (right click and select paste) (or ctrl+v)
Now, on ur phone, roll down statusbar, click usb, select turn off.
Unplug cable
Profit