I'm in the middle of this project on my 98' Sable. Here's what I did:
Ran 2 gauge wire (4 gauge is too small) from the BATT post of the Megafuse panel underhood, across header panel, along passenger fender, down, and along the fuel lines, then up into the trunk using the grommet in the trunk floor, right behind the passenger tire. I covered the wire using 3/8" split loom and 1/2" split loom for double protection, all the way back. You'll need to put a ring terminal on the Megafuse end of the wire, as well as one on the positive wire from the starter motor. That wire will be connected to the BATT post as well. For safety's sake, use a heavy duty fuse within 12" of the positive terminal of the battery. I went to waytekwire.com and grabbed a Megafuse holder and 200 amp fuse.
I have 2 gauge wire from the battery ground to the passenger side rear seatbelt anchor.
I'm using a Sears Diehard Gold battery. If you choose to use a wet cell battery, rather than a dry cell (Optima, Odyssey), you need to use a sealed battery box with a vent tube. The Summit Racing boxes are cheap crap, but cost over $100. There's a couple of sellers on eBay that sell custom made ones for about $60. You just need to drill the wire holes and put the vent tube in. Search for "aluminum battery box".
The other thing that I'm doing is upgrading the wire from the alternator to the ALT post on the Megafuse panel. It's currently 6 gauge wire, but I'm going up to 4 gauge.
JR
