Most of the card editing images available on the Inn are in Photoshop format. If you're willing to
jump through a few hoops, you may be able to download an older version of Photoshop and use that for editing purposes.
If you don't want to do that, and can't edit .PSD files in any other way (not that this is difficult; the free software Paint.NET has a Photoshop plugin available that lets you open .PSDs), the next best thing would be to find or request some 300px JPEG or PNG images of blank cards, import them to Word as images (or perhaps as shapes with an image background) and write text on top of them.