XL97 Wkshts Disappear using Windows 2000

When I open an existing “mutiple worksheet” Excel spreadsheet using a computer running Windows 2000 Professional, all of the worksheets are combined into one. No other worksheet tabs are available from that point on. Has anyone experienced this problem and/or have any solutions to rectify it? Most of the user’s run Windows 98 OS with Office 97 Suite. The test computers running Windows 2000 are also using Office 97.