No, this can't possibly work since 2 systems can't access the same underlying filesystem at the same time. It would corrupt itself immediately.

Some time ago I had some version of linux on a partition that I could start either native or from VMware inside Windows (installed on another partition). One day I forgot I had suspended linux inside VMware and ran it native. It did fsck (because the system was actually not shutdown properly from it's point of view) and everything would be ok if I hadn't resumed the image later and shut it down. Afterwards the system was hopelessly corrupted... (an interesting note is that I had some test version of reiserfs and after some tree restoring I could see most of the files again, but since I didn't need anything anyway, I just deleted the whole thing after a while).

You'd have two operating systems writing to the same disk blocks, so it would just corrupt everything. Since this is Dosbox forum and if you're talking about Windows 3.x, it might work since AFAIK that does not access the file system directly but through the emulated DOS.

And, if you would boot windows (95) with virtual memory disabled both in the host and guest systems?

Again, it would corrupt the file system. Keep in mind that Windows creates a lot of temporary files, the pagefile is not the only file written to disk. Also, Windows 95 requires virtual memory... most times I've disabled virtual memory in Windows, it crashes even if it has plenty RAM to play with.