All right?

The most common form of greeting around here is "you all right?" The first time I heard it I was at a temp agency. Up until that moment I was fine, but I was soon making a mental list of why I was not 'all right'. I think I managed to mutter 'ok thanks' though he had already had his back towards me at that point, which I thought was just rude, but I've since learned it's not always meant to be answered. The second time was again from another temp agency, and I responded 'fine thank you, how are you.' Her response suggested that was not the correct thing to say on my part. At that point I had figured out that it was a greeting, and that I shouldn't freak out when asked if I'm "aayt". But I had forgotten that lesson at a day-temp job which was truly stressfull, and I became increasingly more stressed as people repeatedly came in asking if I was allright. What do they say when they are trully interested? I have no idea. I had suggested to Jessamy that she ask a classmate how to resond, but she's forgotten, and I've been to shy to ask the grocery clerk.

Thanks goodness for the internet.
One site suggested that you say absolutely nothing, another said that 'ok' was also not a good response.
Here's the most comprehensive answer so far:
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Alright
A contraction of "All right": a (usually friendly) British informal greeting, not always accompanied by the word "mate". It can be used (and this is not an exhaustive list) on its own, followed by the word "mate", or followed by a name: this latter usage is usually more friendly than the others, as it implies that you know that person well enough to use their first name in a cheerful and informal greeting.

It can also be used when questioning the wellbeing of another. However, this will almost always be preceeded by a word denoting that it is a question, e.g. "you".

N.B. If someone passes you and says "Alright", do not respond "Yes". There are a number of accepted responses, such as a simple "Alright", often followed by the person in question's name, the phrase normally spoken in a more assertive tone, as it is a response, not a question.

1. Alright mate
2. Alright Alex
3. Alright
4. You alright?
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All right.