A. A. Windows 98 supports 2 file systems, FAT and FAT32. Windows NT 4.0 supports 2 main file systems FAT and NTFS. The only common file system is FAT which means the active partition, C:, must be FAT.
If you then partition the harddisk into one partition for the active partition, one for 98 (d:) and one for NT (e:) you could have FAT32 on D: and NTFS on E: but you should be aware that the 2 operating systems will not be able to see the partition of the other. If you ever want a partition that can be seen by both you will need FAT.
Windows NT 5.0 introduces support for FAT32 so in this case the active partition could be FAT32 and you would only need one separate partition for NT if you wanted NTFS.
There are tools that enable Windows 9x to read NTFS, e.g. NTFSDOS from http://www.sysinternals.com however these are mainly readonly and I may lead to corruption if not used correctly. Also bear in mind Windows NT 5.0 introduces NTFS 5.0 which these utilities will not be able to read.