Use your desktop file manager to change permissions.

OK that did it, i had to create the directory where it was set as root because of floppy access. that works now, but i have still one question, howcan i change keyboard settings? what i mean is things like, how long it takes when i hold one button down, until the the digit is displayed many times in a row like aaaaaaaaaaaaaaaaaaaaaaaaaaaa

if you know what i mean?!

change it in source and recompile I think.

OK, what do i have to chenge to what here?

case CMD_SETTYPERATE:
{
static const int delay[] = { 250, 500, 750, 1000 };
static const int repeat[] =
{ 33,37,42,46,50,54,58,63,67,75,83,92,100,
109,118,125,133,149,167,182,200,217,233,
250,270,303,333,370,400,435,476,500 };
keyb.repeat.pause = delay[(val>>5)&3];
keyb.repeat.rate = repeat[val&0x1f];
keyb.command=CMD_NONE;
}

So dosbox does support different rates, try
http://www.google.de/search?q=dos+utility+set+repeat+rate

For the default setting, use the entries at the bottom of the same source
file where you find
keyb.repeat.pause=500;
and so on, there you can customize the default delay and repeat rate
at wish without a dos utility (which should work as well, but never
tried this).

OK thanks to all, i found an utility that works, and now tetris is playable. actually i only reached 10100 points, buut now i am able to do some training...