Slojmn1,
I have the same camera. All the pictures on my website are taken with a Sony DSC-S70 It's a good camera, but not the ideal camera for tank macros since it tends to want to automate everything. Pictures of fish are the hardest, unless it's a goby that's willing to sit still for you. I've taken lots of blurry pics of percs myself.
One technique you might try is to partially press the shutter and allow it to autofocus on the live rock, then move the camera back a little so that fish are in focus before snapping the picture. I have had little luck using the manual focus for fish.
Another trick is to take the pictures from a greater distance and at a higher resolution. You can then use the software you got with the camera to crop out the part that you want. I generally take mine in 1600x1200 or higher mode and crop down to a 512x384 or 640x480 final size.
Lastly, take lots of pictures and some are going to come out better than others. That's the great thing about digital cameras, you can take a hundred shots and throw out 98 of them to get the perfect shot. I'm still trying to get decent pictures of my 6-line wrasse!
--- Ken