When you click on windows start button|All programs, you'll see a Start Up
folder.
You can create a shortcut to your workbook (*.xl*) and place it there.
In WinXP Home, I'd do this:
Open windows explorer
Traverse to the folder that holds that excel file
select the file
Rightclick on it and choose Copy
Then...
Rightclick on the Windows Start button. Choose Open
Double click on the Programs folder.
Double click on the StartUp Folder
Rightclick on an empty spot and choose Paste Shortcut