is there any difference in reformatting a hard drive on 98 and XP?
Yup, there are lots of difference.
Win98 only runs of fat32 while WinXP can run on fat32 or NTFS. In XP you have to choose from fat32 or ntfs.

There are lots of tutorial on the web on how to format a hard disk. Try searching the web or try this site http://www.pcguide.com/proc/setup/hdd-c.html