New Arduino - Uploading error...Help?

I got an Arduino the other day and have been playing around with it using a RGB LED matrix. I could upload a couple of sketches and then all of the sudden I'm getting this error:

Binary sketch size: 1112 bytes (of a 30720 byte maximum)
/Users/stevenwright/Desktop/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avrdude -C/Users/stevenwright/Desktop/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf -v -v -v -v -pm328p -cstk500v1 -P/dev/tty.usbserial-A8008Iyx -b57600 -D -Uflash:w:/Users/stevenwright/Documents/Arduino/sketch_sep26a/applet/sketch_sep26a.cpp.hex:i

avrdude: Version 5.4-arduino, compiled on Oct 9 2007 at 11:20:31

System wide configuration file is "/Users/stevenwright/Desktop/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf"
User configuration file is "/Users/stevenwright/.avrduderc"
User configuration file does not exist or is not a regular file, skipping

Using Port : /dev/tty.usbserial-A8008Iyx
Using Programmer : stk500v1
Overriding Baud Rate : 57600
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude: Send: Q [51] [20]
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding

Using MAC OSX 10.5, Intel Core 2 Duo
Arduino duemilanove
I could upload for a while and now nothing. Just get the above error. Connecting it to my USB drive on my macbook pro.