Cool air down to several degrees Kelvin...as the temp. drops from room temp.,different gases will condense at different temps. For example, the diatomic nitrogen (N2) will condense at around 75 Kelvin, oxygen at 96 K (i think, but i know where to look this up if i needed to know it exactly) . He condenses at just a few degress above absolute zero. you can look up its one atmosphere condensation point in a book. look up helium in a REFERENCE book (ENCARTA??)

That's a good question.I'm not sure of the answer , but I have a guess. Let's see if we can help each other out. For starters, did you know that air is made up of different gases like nitrogen, oxygen, carbon dioxide and helium? Also, did you know that each of these gases will turn into liquid if you cool them enough (carbon dioxide is a little strange, but we won't talk about that)? It's true...if you take oxygen gas an make it really really cold, it will turn into liquid oxygen. The same is true of nitrogen. Squeezing the gases really really hard will do the same thing....turn the gases into lquids.
So, now we know that gases can turn into liquids. Did you also know that each gas has it's own temperature at which is turns from a gas to a liquid? Did you also know that turning helium into a liquid needs the lowest temperature? That means if we take air (which is made of mainly of nitrogen, oxygen, carbon dioixde and helium) and make it really cold the gases will turn into liquids. First, I think it starts with carbon dioxide (at -78 degrees Celsius), oxygen (at -182 degrees Celsius), and then nitrogen (at -195 degrees Celsius). At -195 degrees Celsius, the other main gases are all liquids and you can pour them out the bottom of your container. 99% of the gas that's left is helium (since it turns to liquid at -268 degress Celsius, -195 degrees Celsius is still really warm for Helium).
So, that's my guess. I'm pretty sure that cooling air down to -195 degrees Celsius would work, leaving helium as the major gas that's left. Of course, maybe there's a cheaper way to do it. Did you know that there are companies which specialize in extracting helium and other gases from the atmosphere? One of the biggest companies that does this is called PraxAir. I bet you could find them on the web if you searched under "helium gas" or "liquid nitrogen." Why don't you try and find them and see if our answer is correct!

Helium is not extracted from the atmosphere. It is separated from natural gas in oil & gas drilling operations. I don't know what methods are specifically used but one example of gas separation technology is microporous membranes. Look up these words in a dictionary if you want to know what this is: "micro", "porous", and "membrane". There is a lot of information on the internet if you want to know more.

I think I have an answer regarding the He question. From my understanding, He is usually purified from natural gas deposits in the course of refining. There is little He in the atmosphere as it has such a low density it tends to dissipate into space. However, He is a common product of radioactive decay of uranium to lead, and the He tends to accumulate in the same natural reserviors underground in which natural gas is found.

I don't think anyone does. The amount of helium in the atmosphere is too small. Instead, helium, I believe, is recovered where oil is found. Somehow, helium slowly collects in these places over time as heavy elements radioactively decay. When people drill for oil they can recover the helium that's trapped with the oil.

Many gases can be recovered from the atmosphere. One easy way to do this is to liquify and separate out various gases from air such as nitrogen, oxygen, and argon.