Possible ways to change radio

I still have the original radio/cassette player in my 1998 SL1, it is one of those with the rounded top corners. The tape player died some time ago but the radio still works. I've thought about doing at least one of the following:
1 - Repairing it.
2 - Getting a CD player (no radio) to go in the space under it.
3 - Replacing it with a new one.
I bought a Haynes Repair Manual for the car to learn things, it states that to take off the panel around the radio, I first need to disconnect the negative terminal on the car battery. Why would I need to do that?
I've seen radio/CD players, is there CD players available with no radio?
If I replace it, how do I given the rounded top corners?
Thanks.

Eric

Removing the radio in a Saturn is ridiculously easy. What you need to do is buy a replacement unit with a CD player and just get rid of the old original one. You can buy an install kit that is specific to your vehicle that will make wiring easy and make it look nice also.

You disconnect the battery so you don't short stuff out and let the smoke out of the electrical components. Please disconnect the negative cable, not the positive. You can blow stuff up if you start wrenching on the positive cable and accidentally touch ground with your wrench.

Replacing the radio on most vehicles, let alone a saturn is really easy. You just need a dash kit (i think there is two available for your car) and a wiring harness. If you're nervous about shopping and installing an aftermarket CD player, then I strongly suggest you shop at www.crutchfield.com. They are one of the most expensive online shops (well, they sell items at full MSRP) but you get the harnesses, dash kits, instructions, etc. for free with your deck and usually arrives pretty quickly. Plus you can return within 30 days if you don't like it (but i'm sure you will) and prepaid shipping labels are included.