I've tried to to connect my Arduino Pro Mini to Gameduino2. I've got this to work by connecting all the required Arduino pins to the Gameduino2. I've also connected a ethernet shield to the SPI bus, with pin 10 as select. This combination works as long as there is no SD card in the Gameduino2. If there IS a SD card in the Gameduino2 I have problems getting everything to work. Removing the SPI connection between Arduino and ethernet shield makes it work again (even with SD card).
Thanks, However, I think I've found the problem. Until today, I've uploaded the sketches to Arduino Pro Mini using a Arduino UNO (without the processor). Today I got the USB/TTL converter and uses it instead of UNO. Then it seems to work. The theory is that the SPI bus "collided" with devices on the UNO itself ! Sounds reasonable ?