Yet another way to do it, if you are on Windows Vista or Windows 7, is to use the Windows Task Scheduler. This provides more control over the precise load time and order of the task.
1. Go to Start and type "Task Scheduler". Hit Enter and approve the UAC prompt if you get one. Then, in the Task Scheduler window that appears, click the Create Basic Task button on the right. (Note: You can select a folder in the tree first to use for organizing your tasks if you want. This has no impact on how the tasks work, it is just for organizational purposes.)
2. In the Create a Basic Task dialog that appears, enter a Name for your task (like "Start MC in TheaterView") and a description if you want. Click Next.
3. Choose "When I log on" as the trigger and click Next.
4. Choose Start a program and click next.
5. Type MC14.exe (no path required) in the Program/script box, and then in the arguments box put: /Mode Theater. Click Next.
6. On the last page, check the "Open the Properties dialog" box and click Finish. This will open the advanced properties dialog for your new task. Note that sometimes the Task Scheduler UI is dumb and this new dialog will open BEHIND the main Task Scheduler UI. Look in your Task Bar for a new item named "Start MC in TheaterView" or whatever you named the task.
7. In the Properties Dialog, you can switch to the Triggers tab and add a delay of 30 seconds or 1 minute. This will allow your computer to finish loading it's normal startup tasks first before trying to load MC's UI. I've found this helps prevent MC from initially marking all of the files as missing if you have media on a remote network share. The properties dialog also keeps a log of the tasks, which is useful if something goes wrong to try to diagnose the error.