Trouble uploading to Arduino NG ('TX' flashing rapidly)


I just broke out my old Arduino NG rev.c (Atmega 168) and I can't seem to upload sketches.

On a Mac: Board: "Arduino NG or older w/ ATmega168" Serial Port: "/dev/tty.usbserial-BLAHBLAHBLAH"

When I click upload, 'RX' and 'TX' flash once, then 'TX' begins to flash rapidly and doesn't stop. The program on the computer says the "Binary sketch size" and the Uploading... status bar never finishes. If I press the reset button on the Arduino while this is happening, I get "avrdude: stk500_getsync(): not in sync: resp=0x10".

Any help is appreciated!

If it helps, I get the same behavior with a different computer. Does a flashing TX mean anything particular about the Arduino?