If mint4win uses
wubildr to boot (which I believe it does), then it's not possible to install and use both (without some manual linking i.e. through a custom grub entry). The
wubildr file is hardcoded to look for
\ubuntu\disks\root.disk with Wubi, and for mint4win I assume it's
\linuxmint\disks\root.disk. So you'd have to switch
wubildr to boot different versions (even if you had two entries in the windows boot manager it would always boot one of either Mint or Ubuntu - the one you installed last).
There may also be conflicts in the registry entries (but this seems more likely to be separate due to the different installer name, so not a problem).
So to explain how Wubi/Mint4win boots:
- Windows boot manager calls
wubildr.mbr. This can be within
\ubuntu\winboot for Win7/Vista (or in
C:\ for XP).
wubildr.mbr searches all partitions for the first
wubildr it finds. This is always in the root of the partition (so can be only one).
wubildr is hardcoded to look for either
\ubuntu\disks\root.disk (for Ubuntu) or
\linuxmint\disks\root.disk (for Mint).
In theory, assuming there are no other conflicts, you could install both Wubi and Mint4Win, but it will always boot the most recently installed. You could then add a custom grub boot entry to boot the other install. But this sort of thing isn't usual for the typical Wubi/Mint4Win user.