If the images are non transparent then a more accessible way is to place the images on top of the text to hide them. That means that if css is turned off or images are turned off then you still get the text unlike the text-indent method that fails if css is on and images are off and you get a blank screen.
I can help you,
if you are building nav bar you should use list with links. Basically what you have done with text indent will help you now. You need to create list of items for nav bar, Each list item will contain link. Link will have background with image so you can create rollover with css that works in every browser and you can hide your text.