When you set a rollover, whatever change you make affects the entire layer, not just the slice you've made. So if all your text is on one layer, and your rollover is supposed to make that text get a drop-shadow, even if your rollover is set for the first word, the entire layer will get that drop-shadow. You need to have every separate rollover piece and rollover state set up as a separate layer. Read up on using sets to help keep all those layers organized -- they're wonderful things.
That will also allow you to change color. Create one layer of the word "Foo" in black; copy the layer and change the color to white. Then you can use your rollover to switch between the two layers by cutting off their visibility.