So with the help of the code from #Portable Trollmaster 3000 I was able to set up the module in no time. It works on the atmega32 (no real surprise here). I've made some little changes to the program - I set the sending power all the way up with the help of the datasheet and also worked on the following function. This should make it easier to set the frequency.

void set_frequency(unsigned long frequency)
{
  unsigned long factor = frequency / 8192;
  unsigned int upper = (uint8_t) (factor >> 8);
  unsigned int lower = (uint8_t) ((factor << 8) >>8);
  
  Wire.beginTransmission(NS731_I2C_addr);
  Wire.write((uint8_t) 0x0a);     
  Wire.write((uint8_t) lower);    // lower 0XEA is 90.0 Mhz 77 / 33 for 108
  Wire.write((uint8_t) upper);    // upper 0X2A Change those values to change the frequency
  Wire.endTransmission(); 
}

updated function, removed not needed type castings etc. (thanks to @al1 )

void set_frequency(unsigned long frequency)
{
  unsigned long factor = frequency / 8192;
  uint8_t upper = factor >> 8;
  uint8_t lower = factor;
  
  Wire.beginTransmission(NS731_I2C_addr);
  Wire.write((uint8_t) 0x0a);     
  Wire.write(lower);    // lower 0XEA is 90.0 Mhz 77 / 33 for 108
  Wire.write(upper);    // upper 0X2A Change those values to change the frequency
  Wire.endTransmission(); 
}