Originally Posted by
Photon
Yes you're right. Quite a few countries are part of what's called the visa waiver program. Basically you can just fill out a green piece of paper on the flight over and you will get an i-20 on arrival. Most civilized countries have this arrangement with the US.
You might need to register online these days before coming over (heard something about it, but its been some time since I was in the US last). However you don't need an embassy visit unless you're doing real flight training at a school etc (then you might need a M visa or M-1, F-1 etc)
The I 20 you fill out grants you permission into the USA as a tourist not to do flight training. I'm a aware many countries do not need a visa to enter the USA but none of them will allow flight training without changing your status. I'm sure you will find someone that will rent to your friend but you will have a difficult time finding someone. When I did a BFR they wouldn't fly with me until I was able to prove my citizenship. Another FBO I rented from to get checked out in a 172 also required my passport before we started.