Zamzar is an online service that converts a humongous number of different file formats – it’s worth trying out if someone sends you an attachment that you can’t open – or you need to convert between different office/av/audio/multimedia formats.
The caveat is that it shouldn’t be used to convert confidential files/documents, as the converted file is left on their servers on a publicly accessible page for a day (it’d be pretty unlikely that anyone would find it, but still.)
