The computer on my 2004 LS V8 is under the dash behind the glove box, up high, it is about the size of a large hard bound book and is obvious. It is against the firewall and from what I can tell actually goes thru it. You can remove it from the engine side by going thru the cabin air filter box on the passenger side under the windshield plastic cowling.
BUT, using a mirror, I have not been able to find any numbers that look like the code for the keyless entry key pad. There was a thread about a year ago on this claiming the code is on the computer, problem is there are several computers in this car. The consensus is that the computer in question is actually in the driver door and should have the codes on it. I plan to look but haven't had the time. I hear it is relatively easy to remove the door panel.
I also read that the code can be found on the trunk hinge struts. Not on mine but others claim to have found it.
Good Luck,
Jim Henderson