Rather than use images with transparencies, it is often preferable to replace transparent pixels with a suitable background colour.
In ACDSee 4, the background colour of transparent PNG files (or any other image file that supports transparency) is by default set to black. There is no immediately apparent option whereby you can change this colour and then save the file as a JPG or similar. After some asking around, I was told that while it is possible to customise this colour, it's a bit of a pain. Here's how: