The partition(s) on your XP computer can stay as NTFS, and your 98 computers can stay as FAT32. You're networking them and there is no problem in reading or transferring data between them.
You haven't shown us a link to the article, but from what you've said, I think it's talking about 2 operating systems on the same computer, in which case, each OS should be installed on its own partition. This is not your case.
Basically you only need to create partitions if that's what you want.
Volume - not sure about the terminology, but yes, you can treat it for practical purposes as a partition (in certain versions of Windows, you can create "volumes" which are not partitions - but you can ignore that).
Windows XP cannot format a partition larger than 32GB in FAT32. You need to use a 98 floppy to fdisk and format such a partition in FAT32. After that, XP can still read and write to the partition.
XP has no 32GB limit if you want to format the partition in NTFS.
The theoretical max sizes for FAT32 and NTFS partitions are much much larger than the disk sizes you normally come across. They're at least in Terabytes.