HelenD,
Did you put a password on the directories and printers you are sharing? If not then you could create accounts on the WinXP Comp which the Win98 Comps can use to log in with to the WinXP Comp.
In Win98 you can set the computers to log in to the WinXP Comp each time the Win98 Comp boots, using the Username and Password.
Take Care,
Richard