..I had a music teacher back in high school..he was kinda a dick, but he had perfect pitch. He was a great guy after I got to know him, but one of the reasons, looking back, was that he was a world class musician teaching our 'metal shop' classical guitar class first thing in the morning (only B I got in high school!)...you could burp, blow over an empty pop bottle for a tone, fart, do ANYTHING, and this guy could play the same note back to you on the trombone, his preferred instrument (.."superior instrument" as he called it).
I borrowed some tapes from a friend years back with the Burges method. It was interesting, and after the first tape I could pick out a seventh interval...but like the tapes say, it's just the tip of the iceberg...to really get it, you'd need to study for a long hard time, I would think. I didn't get past the first few tapes.
The thing about perfect pitch is this...if you're born with it, then without some kinda of instruction to what a G or D note even is, how can you use it?..I've heard of the naturals who just sit at a piano at 3 years old, plink away a few days, then start playing songs off the radio...our teacher could do this by hearing his kids play Super Mario Bros, then play it in class for laughs. You need to have some kind of musical instruction for this gift to come to fruition.
It can be a double edged sword, too...our teacher would come into the room with his hands over his ears, and one day cracked on us and told us what a nightmare it was to hear our noise down the hall..."I wish you could wear these ears for one day!" he'd say...what I think he meant was, since he could hear all the inconsistencies, it would drive him crazy!...when the music was in tune and all that, it was great, but when it was bad, it was really bad!..and you can't get away from that gift.
One cool thing was he could tune a guitar is about 5 seconds..pluck an open string by itself, next and so on....and each string ONCE...and the thing was in tune.
The CD's you're mentioning are pricey, but if you think it's worth it, just be aware that you're going to spend a LOT of time applying it. If you have the time and energy, go for it. It's like a book on memory technique or speed reading...you have to practice a lot to make it happen....time which you might spend more wisely on guitar practice....up to you.