Unfortunately there isn't an easy work-around for this. I had no idea that Hard Mix was not present in PS7. There are two "kind-of" work-arounds; one is to use Image-Adjustments-Threshold and the other is to use Brightness/Contrast. When I first started doing this sort of stuff I didn't know about hard mix so here is what I used to do: On a new layer I use a low opacity airbrush (black for ocean and white for land) mainly to connect land chunks (the lighter areas) and make a black frame around the land chunks. Once you have something you're happy with then merge the layers and apply either threshold or contrast and continue from there. If you'd like I could throw up some screenshots tomorrow evening.