It sounds as though you are encountering the differences in file systems on your various disks.
Most really old PC stuff used "FAT Format." More recent versions of Windows stuff generally could use the older FAT, but the trend has been to convert everything to "FAT32."
Windows NT - or just NT - I believe (not checked on this recently) could read FAT of FAT32 disks(?), but the preference was that they use a newer disk layout called "NTFS(?)."
I'm not really up on what formts the various Unix/Linux flavors use now, but it's almost certainly something else.
The problem is, probably, that each of your disks/partitions is written in a "different language," that the other systems can't read.
In Windows Explorer, you can right click on a drive and look at properties, and it sould tell you which format is being used by any drive you can see. I'm not sure how you verify for Unix.
Windows doesn't usually have too much trouble "connecting" to "foreign format" drives that use other Windows formats. (I assume that in Windows Explorer you've done the "Tools - map drive" thingy?)
A recommendation I've seen (but haven't needed) is that multi-boot systems should have each op system on a separate drive, but that all data - or other stuff you want to share between the op systems should be on a separate drive/partition. If you can find one format that all of your op systems can read, then use it for the "data drive."
I can't claim much experience in this area, since I don't have anything "Nixy" on my system, but maybe this will get some discussion started.