wanted: a computer simulation program
the program should run on any windows xp / 2000 computer

it's a simulation on the predator-prey principle.

the principle:
in a square (size: input) there are a number (input) of red, blue and
green balls. They move at random within the square. if they bounce to
one of the borders of the square they bounce back in the same angle.
their speed is all the same. if two balls 'meet' each other the
following rule applies:
- blue meets red: 2 blue balls go further
- red meets green: two red balls go further
- green meets blue: two green balls go further

the user sees:
- the square, with all balls moving. number of balls per color is
between 1 and 100. so: maximum 300 balls should be able to move in the
square (bigger square?)

- a dynamic graphical representation of the number of blue, red and green balls
horizontal axis: time
vertical axes: number of balls
and three lines (red, blue, green) move dynamiccally from left (time -
start) to right, just until one color remains (which will always
happen)

clear enough??

Sounds like a Computer Science student needs his/her assignment done
for $50. I would start hanging out in your computer lab. Someone might
do it for a keg of beer.

no, i'm not a computer science student. 
just would like to use the program in a presentation.

In which language do you need it to be done.
Will VB.NET be OK?

i don't care; as long as it runs on windows 2000/xp computers.
and it has to run fast, so a simulation with 200 balls of each color
should be possible

Its worth more...and not really $50.