"Windows NT 4 does not like anything other than FAT16 and NTFS, so you're not going to get what you want out of this, unless you go Windows 2000 instead of NT 4 (if that 2GB barrier is really a problem).
EDIT: If you're using VMWare, why do you want the two OSes to share a single drive anyway? That makes little sense to me.
Create a boot partition with 2GB and FAT16. Create a second partition for Windows 98 and FAT32. Create a third partition for Windows NT 4 and NTFS.
Install Windows 98 into the D: drive (i.e. FAT32 partition), and NTFS into the third partition (which it will probably call D: as well, but should call E:).
You'll need a big C: drive because some installers are stupid and like putting rubbish on the C: drive, regardless of where Windows is. Case in point is Visual Studio 6."