yes, as a previous answer said, it is probably RAW format they were taken in. I used to have a Canon Digital SLR and it came with software to view and adjust the RAW files. Did your camera come with a disk containing some software to do the same? If so put it in and then you should be able to open them and convert them to jpg files.
Alternatively you can try (and I do not know if this is possible either in batch or one at a time), try viewing the images on the camera and have a look in the options when viewing to convert them to jpg files. Save them on the card and they should be able to be seen.
The only thing that worries me is that with my Canon I could see the RAW files in Windows, no icon on them, couldn't open them until I installed the software, but I could see them.
Google how to view (camera brand) raw files in explorer in (windows version), there are some things you can download to do this as I had one for Canon RAW files once.
example "How to view Canon raw files in Explorer Vista
Last resort would be to go to somewhere like Jessops, I am sure they'd be able to get them printed as is for you somehow,
Hope you get the photos sorted.