I'm on a iMac Retina 64 bit chipset with OS 10.10.5. Uplink is not working for me either. I'd suppose it has something to do with the chip being x64 instead of x32.
I'd like to get a response from Ambrosia though. Getting the game updated would be very nice. The GUI doesn't need much, part of the allure of this game is it's simplicity and need to use your imagination or written notes.