That is done with a mask. Apply a gradient to the mask will make one side of the image transparent. If the layer below the image is white, it will blend to white, if it is black, well I think you get the idea.
Then add your text to a layer above the image.
In this case, you would end up with three layers.
If you would like to change this at a later date, I recommend you save in a format like psd or tiff that support transparency and layers. Png supports only transparency and not layers, finally jpg does not support layers or transparency but has a high compression for sending over email or the web.
I hope this helps.