1. My recollection is there is a restriction on how large the "system" partition can be when installing NT 4.0 from the distribution media. (Or is it the partition where the operating system is installed to?). I believe this is either 2 GB or 4 GB. Probably 2 GByte because I believe you want to format it FAT16.
You loaded Windows 98 SE first onto your primary partition, a 10 GByte partition formated FAT32. This "active" primary partition is now the "system" volume, your "C:" Drive.
A couple of mistakes here. Your system volume is too large. It is also formatted in a file system NT 4.0 can't read (only reads FAT16 or NTFS). Suggest you start over.
2. Recommendation. Suggest the following:
a. Create Primary Partition, 2 GBytes maximum formatted FAT16 to be your system volume, the c: drive.
b. Create Extended Partition to almost use rest of hard drive (leave couple MegaBytes free)
c. Within Extended partition create 10 GByte logical drive formatted FAT32 to hold Windows 98 SE in d: drive.
d. Do "custom" installation of Windows 98 SE to install operating system to "D:\Windows" directory. The system files needed to boot Windows 98 SE (about four files; msdos.sys, config.sys, command.com,
) will automatically install to the C: drive.
e. Create another logical volume within extended partition for Windows NT4.0 installation (Format as FAT16 or NTFS; your choice, but Windows 98 SE can read FAT16, not NTFS). Install Windows NT4.0. Like Windows 98 SE, its system boot files will also automatically install to C: drive.
f. Create another logical volume within extended partition for Windows 2000 Pro (Format as FAT16, FAT32, or NTFS). Install Windows 2000 Pro to this volume. Its system boot files will also automatically install to system volume c:.
Note: If you want a "common" data volume, it should be formatted in a file system all three systems can read (i.e. FAT16). Might want to place it after c: volume (as d: volume?) so all operating systems can read it and reference all preceding volumes with same letters. If your operating system doesn't recognize a file system (FAT16, FAT32, NTFS, or whatever), it won't assign drive letter to it.
3. So...
Primary Partition (Active)
C: System_Vol 2 GByte maximum (FAT16)
Extended Partition
D: Data_Vol 2 GByte (FAT16)
E: Win98_SE 10 GByte (FAT32)
F: WinNT_40 ?? GByte (FAT16 or NTFS; probably NTFS?)
G: Win2000_Pro ?? GByte (FAT16, FAT32, or NTFS; probably NTFS?)