No welcome page after installing to subdomain

My 5-minute installation of WP 2.8 dragged on for a couple days, because of a very elementary mistake.

I was installing WP to the root of a subdomain– or rather, since I’m using Plesk, installing to the httpdocs folder. When I pointed my browser to wp-admin/install.php, no Welcome page appeared. Instead, the browser offered to open or save the install.php file.

I did the usual troubleshooting, Googling, and forum-browsing. Finally, one clue took root in my mind. Someone in the WP support forums had had the very same complaint, and the problem was that her PHP support wasn’t activated.

Well, I had assumed mine was turned on, since I’m using PHP to deliver slideshows from my main site. But when I checked the Plesk controls for my subdomain, it turned out that its PHP support had to be turned on separately. And voila! There’s my Welcome page!

I hope this story saves somebody else from wasting a bunch of time like I did.