Ryan, I replaced the steering cable on my 03 SSV a couple weeks ago. I had the same problems you are having. It will get worse to the point where it takes two hands to turn the boat even at speed. It's a pretty easy fix though.
First disconnect the steering cable from the rudder. You should be able to easily turn the rudder by hand with it disconnected. If you can't the rudder assembly is bad and needs to be replaced. If it does turn easily you need to replace your steering cable.
Take the back seat and v-drive cover out. Then remove the two floor panels, there are screws in the corners. You might need to feel around for them a little the carpet might be covering the screw heads. Then you'll want to pull the front wall of the drivers footwell out. Again the screws will be in the corners. You'll also want to pull the wall out of the rear compartment on the passenger side so you can reach the cable at the rudder.
Once you have all that out it's pretty simple to replace the cable. Disconnect the rack from the back of the helm and pull the old cable out from the front.
Then feed your new one in, there is a hole that it runs down through behind the wall in the foot well that you removed. That runs into a kind of conduit that runs back towards the gas tank. It should be a pretty easy feed. Just have a buddy watch for it to come out the other side and then pull it to the back. Hook it up to the rudder assembly, and to the back of the wheel. Put the floors back in and you're done.
The whole thing took two of us about an hour and a half. I had read that you should tie a string to the old one when you pull it out. But if you pull the floors you don't need to do that. It takes about 5 minutes to get the floors out of there so it's worth pulling them from the start. There is only about a two foot run from the hole in the front under the drivers seat that you won't be able to see the cable. And that part is running through a built in passage so you really can't miss.
Here's the cable you'll need at Ski-Dim http://www.skidim.com/prodinfo.asp?number=TELSSC13420
I got it cheaper from the factory though, the skiers choice part number is 106285
Good luck, shoot me a email or PM if you have any other questions, but that should pretty much cover you.