In order to use these tunings, you will need a digital strobe tuner with variable cent references. I recommend spending $130 on a Peterson StroboPlus HD...it will make tuning in general one hell of a lot easier and more accurate. It will also make it extremely simple to keep track of any tuning you find and tune to it more or less instantly. There is a free online storage and retrieval of any tuning you find or make up which you can save to the StroboPlus HD or any other Peterson tuner with variable cent offsets. I can't tell you how awesome this is.
You can also get the Peterson digital strobe tuner app for $10 and spend another $6 for their "Sweetened" tuning presets. These presets make your guitar and any stringed instrument sound as in tune all over the neck as possible and your overall guitar sound will change for the better. So for only $16, you can jump in and start using the tunings that I have found.
This thread contains tunings from Van Halen recordings that I have found using my Peterson StroboPlus HD digital strobe tuner. I generally refer to the isolated guitar tracks where possible along with the best available CD releases. I also try to use a guitar that is as physically close to the guitar that Eddie used on the original recordings as possible (at least as far as we know from Eddie's interviews). For example, for "Runnin' With The Devil" and "You Really Got Me" I used my '75-'76 Ibanez Destroyer. For the electric parts of "Ice Cream Man" I used my '78 era Musikraft/Locke Frankenstein with a standard Fender tremolo. For "Girl Gone Bad" I used my '58 reissue Gibson Flying V. For "Panama" I used my black Musikraft 5150 replica...That song may have been recorded with Eddie's '83 era Frankenstein, but I only own one guitar with a Floyd Rose, which is my Musikraft 5150, so I used that guitar as the closest I have to what may have been used on the original recording. I used my 1968 Fender Strat to find and notate the tunings on the recordings like the intros to "Women In Love" and "Hear About It Later" where Eddie used standard strat style guitars with three single coil pickups.
I have used my Peterson to check the tunings all over the neck at various points during the tracks. There are some tracks that actually have different tunings on a different guitar used in an intro versus the rest of the song. For example, the "Women In Love" intro strat is tuned differently from the humbucker equipped guitar used for the main distorted electric parts that occur later in the song.
I'm not interested in the "WHY?" question as to "Why" these tunings exist. This thread is intended to point out that they do indeed exist and to point out as closely as I am able to what the pitches for each of the strings are. All of these tunings assume that you are using a guitar that has been intonated as accurately as possible with a strobe tuner.

Eddie backstage with the Peterson 420 strobe tuner..