I agree with Thorhammer's and Aeon's comments as to the nature of Thelema.
But I think that Abrac's question implies something like "If a country were formed which was composed wholly of Thelemites, what kind of government would that country have?"
Rabelais' idea of the Abbey of Thelema was one of innate nobility. If everybody could do what they wanted, then nobody would interfere with anybody else.
So the first answer is anarchy. Not anarchy tending to feudalism (weaker people gathering around a stronger person), but each individual fully respecting the rights of other individuals to do as they please (because of the innate nobility of the free person). I think Rabelais noted that basic needs would have to provided for, so whatever it took to procure them - work - would be necessary, but beyond that, no buying and no selling, no fights over ownership of things. Call it proto-communism if you like, but without the heavy machinery of industry and finance (as we know them and love them today - this is the 16th century remember, and the Abbey was a Utopia, not a nation-state).
Crowley wrote a lot about government. The first thing I recall is chapter 81 of the Book of Lies (chapter 80, and a few others, are relevant also):
" LOUIS LINGG
I am not an Anarchist in your sense of the word:
your brain is too dense for any known explosive
to affect it.
I am not an Anarchist in your sense of the word:
fancy a Policeman let loose on Society!
While there exists the burgess, the hunting man, or
any man with ideals less than Shelley's and self-
discipline less than Loyola's-in short, any man
who falls far short of MYSELF-I am against
Anarchy, and for Feudalism.
Every "emancipator" has enslaved the free."
So here we see Crowley's idea of ideal anarchy - not quite feasible, he recognizes, ironically.
Then there is the "Scientific Solution to the Problem of Government" (1937). This is a short, complex and subtle document, well worth pondering for the application of Thelema to a system of government. The last line reads:
"The absolute rule of the state shall be a function of the absolute liberty of each individual will."
http://www.geocities.com/nu_isis/sspg.html
Finally, Liber OZ (1941).
http://www.hermetic.com/crowley/libers/lib77.html
This is Crowley's last comprehensive statement of Thelemic anarchy - it resembles in so many ways the UN's Universal Declaration of Human Rights (1948), yet goes beyond it.
Yet in all of these we are still left with the fact that Thorhammer and Aeon point out - most people won't be Thelemites. So there has to be government - imposed order, not "natural" freedom (because most people won't be free - not because Thelemites want to "rule" them, but because of their own ignorance and fear - hence the need for sustained education (as Crowley would say, "Education means 'leading out', not 'stuffing in')).
Thus, I think the answer to the hypothetical question of what a government run by Thelemites would look like is - whatever kind they want to have. I would think, at the very least, Thelemic "rulers" of non-Thelemites would try to curb the power of herd/mob thinking, and promote personal development. Thus a strong police force, and a strong dedication to education. In fact, the best Thelemite society might resemble the progressive Western societies of today, shorn of the power of money and religion to influence policy. I'd like to think Corporatism might be gone also, but I'm not the most sophisticated thinker in this area. The Thelemites I know place a high value on self-reliance, and that seems to go hand in hand with the philosophy of Thelema, so it seems natural that "mass production" (and the money-power that goes with it), as it inclines to herd thinking, tends to be disparaged, and would thus tend to be actively discouraged in a Thelemic government.
Ross