Trouble uploading sketches to arduino board

Hello,

I'm new to using the arduino, got some of the basics down using boards at school. Purchased my own and tried to test it out and I get this message when I try uploading:

avrdude: stk500_getsync(): not in sync: resp=0x20
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x20

The sketch will run for a few second before this message pops up. This occurs each time with whatever I try to upload.

I'm using a Mac w/ the latest OS X update, a Duemilanove, the only program I've loaded recently is the arduino software (13 then updated to 14).

I checked the troubleshooting section as well, and did not see anything.
Thanks for any help.

Did you select the Duemilanove board from the pull-down menu Tools > Board ?

Are you using the Duemilanove with a 328 processor? If so select the board with a 328, not standard Duemilanove.
Mike