I mean the Mint installer, not mint4win. Mint booted from a SD-card, then the installer seems not to be able to detect the Windows8 system on the hard-drive. The "not enough space" warning is issued by Windows. I tried a different procedure I found in a tutorial:
This procedure make Windows8 itself shrink its partition before trying to boot and then install Mint.
I have to setup a development pc for Eclipse (Android) so I do not know if mint4win is suitable because I think the performance of the resulting linux system would be worse.