For descartes, what is that "Archimedeam point" which delivers him
from the skepticism of "readical doubt"?  retrace the cource of
Descartes meditation from radical doubt to the cogito, from the cogito
to the principles of reason from the principle of reason to god and
from god to material things?

Read Deacartes' Second Meditation. A couple of paragrapghs in, he says
that Archimedes (- a Greek engineer who discovered the theory of
leverage) believed that he could move the Earth if only he ha a fixed
point on which to place a lever. Similarly, Descartes believes that if
he could find a fixed point  - in this case some knowledge which is so
certain that it cannot be doubted (and so would resist all the doubts
about knowledge which are listed in the first Meditation) - then he
could make significant discoveries in human knowledge. Descartes then
promptly finds his Archimedean fixed point when he discovers that
'Cogito ergo Sum' ('I think, therefore I exist'). I cannot doubt my
own existence, even if I can be deceived about everything else. After
this, descartes 'proves' the existence of God in Meditations 3 and 5
and posits his theory of Cartesian dualism in Meditation 6. Medtation
6 is where he proves that material things exist.

I'm not going into any more detail because you should write your own
essays and not plagiarise from other people. In any case, you don't
pay enough for a decent essay. But this should help you find your way
through the text.
Amber

it's not somthing that i want to plagiarise in any way. it's the main
question that is going to be on a final of mine, and it's somthing
that i am haveing trouble understanding.