You mean like, if I have "Sheet1", "Sheet2" and "Sheet3", how do I make "Sheet3" be the active sheet when the file is opened? You can do it this way.
1. Right-Click on the Excel icon to the left of the "File" menu.
2. Choose "View Code"
3. Copy and paste this code in:
Private Sub Workbook_Open()
Sheets("Sheet3").Activate
End Sub
The only problems with this are that you'll get a flicker of the first page no matter what you do. If you're not using macros in your workbook then you're substituting one mouse click for another. The user will now have to hit "Enable Macros" on startup.
One really easy way to make a specific page be the active page on startup is to move it to the front of the sheet order. To do this just drag and drop the sheet name tab to the start of the workbook.