WinDVD is only changing the pitch of the sound (no clue about VLC).
You can use the free software ReClock. After installation play a movie with PowerDVD, click the clock symbol and check PAL speeddown.
Note that ReClock needs to be reinstalled whenever you update PowerDVD.

Thanks M8R. I had the idea from somewhere ReClock only worked with Windows' inbuilt Media Player, so I hadn't tried it under PowerDVD, which tends not to play very nicely with other software anyway.

Rather than try to integrate yet another piece of software, I might just stick with VLC (which has the added advantage of sidestepping region coding issues).

But I appreciate your reply. ;