Is there somebody who wants the same?
Is there somebody who do this and want to help me?

I want to replace the bootloader program preprogrammed by Atmel,
with my own bootloader.

For that job, i need a hardware programmer, but i want to
build it myself. It's a very simple interface, single voltage
and some lines to transmit/receive the data.

hardware and schematic See J3 op page 3-9
all 89C5131 files

Who knows more or has a datasheet with the device programming specification?

I know you can program the device with FLIP and USB or UART, but in my case that's not the solution to reprogram the bootloader flash-part.