Step-by-step info:

I'm assuming you're using Windows XP for this next bit.
If you've already double-clicked on a .vpt file (a Visual Pinball table file) and set it to open with Visual Pinball, you'll see it under the Windows Explorer settings -- open a file explorer window (shortcut: Windows + E), choose "Tools - Folder Options" from the menu, and click the "File Types" tab.
After the full list displays (might take a few seconds), find the "VPT" extension, click it, then click the "Advanced" button.
From there, you can change the "default" action Windows will take when you double-click on a file.
Click "open" in the list of possible "actions", and click "Edit..."
Change the part under "Application used to perform action:" from
Visual Pinball\VPinball.exe
to
Visual Pinball\VPinball.exe /Play
Make sure you don't remove the rest of the path name to the Visual Pinball program, or the "" marks...or the %1 , which is the filename Windows will "pass" to Visual Pinball as the table to open and play.
Hope that helps!
