I put it in devs:kickstarts (well c: winuae hd devs kickstarts ) and renamed it to kick40068.a1200, I also put the RTB-File and rom.key in the same directory.
I'm using the amiga-os-310-a1200.rom from Cloanto's Amiga Forever. All kickstarts detected and all kickstarts and rom.key are copied to the Kickstarts folder.