Step 1: Create a desktop shortcut icon to your calendar by:
Right click on an open area on your computer's desktop screen and go to the "New" menu item near the bottom of the menu list.  On the "New" items list choose "Shortcut" near the top of the menu item list.  This should open a screen to create your shortcut.
In the space "Type the location of the item:" enter the following: (substitute your calendar's identifier)  and click the next button.  In the space "Type a name for this shortcut" enter a name for the shortcut then click the Finish button.  You should now have an icon on your desktop that when double-clicked will open your calendar.
Step 2: Put the shortcut into your Startup items folder:
This can be a little tricky.  Click on the "Start" button at the bottom left of your screen.  Go to "Settings" and choose "Taskbar & Start Menu".  On the "Taskbar & Start Menu Properties" screen, select the "Advanced" tab, then click on the "Advanced" button.  You should then see a Windows Explorer view with a list of folders with the "Start Menu" folder highlighted and with the "Programs" folder under.  Use the + sign to open the "Programs" folder and scroll down until you see a folder called "Startup".  Finally, position the window so you can see the shortcut icon you created in step 1 above and then click-hold on that icon and drag it into the "Startup" folder.
You should then be able to restart your computer and your calendar will
open automatically.
These instructions are for Windows 2000. If you are running Windows XP
you may see some items displayed a little differently.