I will go under the turist visa, since its less than 18 hours per week?
Explore, I think you will find that noone here will touch this issue anymore, not even with a bargepole. It's been discussed here without a clear outcome and since getting it wrong might be very costly for some people, we don't want to give a clear yes/no on this anymore.
Let me try to summarize the principles of the US visa process and then tell you where the pain points are. You can then draw your own conclusion on whether to obtain an M-1 visa or not.
First off, the principle is that everyone entering the US has to have a visa. M-1, M-2, B-1, whatever. However, since the US receives so many visitors from Europe and a few other 'western' countries, the process of having all these people apply for a visa would be too involved and costly.
So the US has invented the "Visa Waiver Programme" (VWP). IF you are from any of the qualifying countries, IF you are not a terrorist, AIDS patient or any of the other things that are asked about on the green form, IF you arrive in the US by a scheduled airline or boat service, or overland, and IF your purpose is short-term business or tourism you can apply for the VWP scheme by filling in the green card they hand you in the aircraft. It is then finally up to the friendly INS officer at the airport to decide whether you indeed qualify, and are admitted under the VWP program.
If you do not qualify for the VWP program you have to get a visa of some sort. This means presenting yourself at the embassy, filling in forms, depositing fingerprints and money, and waiting a few days for your passport to be returned. Takes about three hours in total, plus travel time, and getting an appointment might take two months in busy periods, depending also on the type of visa you require.
There are several visa types. One of the visa types is a "tourist visa". This is given to people who visit the US as a tourist but do not apply for the VWP program, for instance because they are not from a qualifying country, or for instance if they enter the US in a way that's not allowed under the VWP (by private aircraft for instance).
(The reason for the latter is that under the VWP, if the INS officer deems that you do not qualify, the airline *has to* fly you back to your country of origin - airlines have to sign contracts to this effect with the US government before they're allowed to transport VWP-qualifying people to the US. This isn't possible for private aircraft, hence people flying in on private aircraft automatically do not qualify for the VWP.)
The most important visa type in the context of flying training is the M-1 visa. This is for short-term study and is *required* if your main purpose for visiting the US is getting trained in something. Now "main purpose" is a rather loose definition and for vocational studies, is interpreted as "more than 18 hours of practical work" per week or "22 hours of classroom studies".
The big issue, to which nobody has been able to answer sufficiently, is whether this 18-hour interpretation also applies to flight training, and if so, what is included in this 18 hours: actual flying only, or pre- and post-flight briefs too? Flight preparation? Ground studies? Self studies?
In any case, if you fly to the US solely to obtain your FAA PPL (and maybe have some fun on the side) it can be argued (and the INS officer will probably do just that) your main purpose, according to the immigration law, is study, not tourism or business, and you therefore have to have an M-1 visa. He can, I think, brush aside the 18-hour requirement as being not applicable in this case. And without a visa, that means you're going home on the next flight.
If you want to go to the US under the VWP for flight training, I'd make damn sure that the INS agrees with this beforehand, by getting their specific interpretation of the law in writing, applicable to your situation. And, obviously, if you don't qualify for the VWP program outright (I have no idea about Norways status for instance) the difference between getting a tourist visa and a student visa is negligeable and not worth this discussion.
Oh, and if you think about dodging the question and just telling the INS that you're going to be a tourist for three weeks, think again. Although the TSA doesn't check your visa status outright (as I understand), it does say in their regulations that they can withhold training permission (and worse) if they find you training without the proper immigration status. This can have serious repercussions, not just for you but for the school as well.