I originally checked out Arduino on my G4, although I hadn't made much use of it then. Another option to using an Uno to program the bootloader is using a dedicated USB AVR ISP adaptor. If you work with AVRs, it is worth having one around. I bought one of these from SparkFun (no affiliation) https://www.olimex.com/Products/AVR/Programmers/AVR-ISP500/ Another option is to only get Arduinos which use the FT232R, which have Mac drivers - sorry, I know that this doesn't help you with the ones you have now. Another option might be to bypass the USB->RS232 chip and apply serial to the RX and TX lines, if your Mac has a serial port.