We should, when possible, use the same interface to get saveasfilename, etc.
On nt, the -confirmonwrite option is neither known or used (whereas on aix/linux, this option is supported).
I added a small patch to this request, that allow to switch on/off the OFN_OVERWRITEPROMPT switch used in tkWinDialogs.c
Regards,
Eloi
patch.confirmoverwrite_nt.diff