Very shortly they wil be part of the OneWorld alliance. Any airline in this alliance will then accept Qatar miles. This includes American Airlines, Cathay, British Airways etc.
All of the major airlines allow you to give your frequent flyer miles to friends and family or transfer the miles to another account holder with the same airline
Yes - they are both part of Star Alliance and have reciprocal arrangements
Most airlines have different procedures for cashing in your frequent flyer miles. Most airlines will now let you redeem them online, when booking a new flight. Or they will issues you a certificate once you have obtained enough redeemable frequent flyer miles.
No, most airlines will not let you convert your frequent flyer miles into cash. This is because the airlines would like for you to fly with them again, and if they instead give you cash then you are able to spend it wherever you would like.
No you can't, they aren't part of the same company.
The individaul airlines websites are definitely the best way
Delta offers frequent flyer miles that they call Delta SkyMiles. You can find out the benefits, rules, and answers to FAQ's at http://www.delta.com/skymiles/index.jsp
With careful planning, this trip can be done for as little as 20,000 United Airlines FF miles.
Typically this would be 100,000 miles round trip.
Any airline in the Skyteam alliance - but particularly with AirFrance and KLM
The program is called OnePass - 25000 gets you silver elite, 50K gets you Gold Elite and 75K gets you Platinum Elite and they have just introduced another tier
You will earn points with each flight you make on American Airlines. You can then redeem the points for flights or for upgrades on flights.