Well i just finished Old World Blues.... Very cool DLC.. Great story, and all that jazz... I read all the computer terminals, well the ones i could find, that shined light on the Siera Madria, but I never found an Awnser to what experiment casued those Zombie guys with Gas Masks in Dead Money... Can somone tell me what that story was all about?

The people in the suits in Sierra madre were originally plain old maitnence/ repair men who worked for the casino/ villa(although I do believe there were 2 separate groups, as you can read in terminals about how they got into fights/ arguments with each other)
Once the red cloud moved in they needed a way to repair machines n such which were engulfed in the cloud. Mr. Sinclair(I think) had the great minds over at Big. MT develop a suit which could handle the gas, or atleast that's what was told to the general public. I'm guessing there was some devious idea behind the suits in the first place, because.....

In a terminal(located where you leave Christine for the Gala) you can read how a group of men, wearing the suits, were sent to check out some problems in the duct work which was covered in the cloud. The men reportedly could not get out of these suits once they finished the job. The only way they(actually only speaks of one man) could escape the suit was due to the Cosmic Knife, which can cut through just about anything.
So, it seems Mr.Sinclair never intended for the suit to come off, or it was someone at Big. MT..... It would make sense as they were creating the lobotomite, which is basically a brain dead soldier. Aswell as them creating the Y-17 override harness(not the correct name)
So it seems they were trying to create some sort of soldier, and the ghosts were simply a stage in that development. Sadly the Sierra Madres workers were being used as guinea pigs, without them knowing.

So in short, they were once the staff of the villa/ casino. Over the years they lost all connections to being human and are now what you see them as.

Hope that answers your question, I know I still have a crap load of my own.

I figured as much.... But there is no Terminal in the Big Empty that talks about these guys?

There may be, but I'm not sure.
Try looking where you can actually get the mask/ suit they use. Forgot where it is exactly, I'm sure YouTube can show ya the way.

The second post practically covered it all.
http://fallout.wikia.com/wiki/Ghost_People
But that should give you more information on them, from people who hopefully knew what they were writing.

One small correction, the suits wouldn't come off because the cloud caused the locks on the suit to errode, not a design/intentional flaw. At least that's what I remember, I'll get back to you on that, coincedentally, I have a character inside the swiching station right now.

just as I read his post, I was thinking, it can't be that he planned for em' never to come out, cause you can get one, and equip/un-equip it...

Mr.Sinclair made a deal with big empty, in exchange for high grade test (like the chips) Sierra madre was to be used as testing ground for many of big emptys new tech like the auto doctors.

they secertly release the Cloud in the city ( i assume some bio weapon) so that they coukd test their new suits and see if they could stop the cloud, ulitmately it did not.....