Once more: Thank you lepricaun!
A tip to 7:
In principle, Nr.7 is "just" somewhat more difficult than
Nr.6, but since the password is somewhat lengthy, one has
to be quite careful while analysing the code in order to
extract the equations to solve for the login/pw.
Double-check each equation you write down. It costs quite
a lot of time to backtrack errors...

As usual in IT, there are several approaches how to crack
the login/pw, eg. change the exe itself, use brute-force
attack, make reasonable guesses (after having parts of the login/pw),
solve non-linear and rather undeterministic equations.
There are also several techniques how to do the reverse
engineering ie. one even can analyse somewhat complicated
arithmetics without knowing any assembler at all (well, just some
basics about the [ebp]).

Since people here seem to be quite interested in participating
in this little game, I guess there might be an interest in a
tutorial about "reverse engineering". I think, using crackit_6
and crackit_7 as examples, I could put together something reasonable.
However, it will be somewhat lengthy, I guess. What do you think?
Would it be spoiling the fun here?