Okay, so this is bizarre...
I've played through the game once and everything was fine, no bugs or anything. Because of the way my monitor tends to make things look (it's a big, high resolution monitor), I alternated between fullscreen and windowed mode--last time I played, it was in fullscreen mode, since the chase sequences are nigh-impossible in windowed. So, when I started up the game today, the first thing I did was turn fullscreen mode off...
...And then the game window disappeared. I can still hear the main menu music playing, and the program shows up in my taskbar, but the actual window is nowhere to be found. And yes, I did check to make sure that it wasn't minimized--clicking on the tab on the taskbar doesn't do anything, and neither does minimizing and then restoring it (well, in theory--I'm doing that from the taskbar tab, but in reality, nothing's happening on my screen, since the window's still vanished).
I've tried fiddling with my screen resolution, quitting and restarting the game itself, even rebooting my system--nothing's worked. Erm. This is not so good. Suggestions, anyone?
Edit: It's just occurred to me that this didn't start happening until I installed a patch for Psychonauts, which also updated my DirectX drivers. What are the chances that that's what's causing it, and if so, what can I do to fix it?