Before you can even upload sketches, you must have the jumper set right. If you want to power it from the DC jack, place the jumper on the DC side of the 3-pin header. If you're going to power it via the FTDI connector, place it in the USB side The jumper is to the left of the RESET button.
OK so now you want to upload code, right? First up, you will need an FTDI Friend or FTDI Cable to talk to the computer via USB. If this is your first time using an FTDI adapter, you will want to follow our little tutorial on downloading and installing the drivers (includes download for FTDI drivers) - drivers are required!
If you're using an FTDI cable, connect it so that the black wire is next to the silkscreen text blk and the green wire is next to the grn text (you can also remember its next to the Green LED. If you're using an FTDI friend, match up the texts (both say black and green)
Connect the FTDI adapter to your computer and start the IDE. Select the COM or /dev/tty port that is created when you plugged in the FTDI adapter
Be sure to select Arduino Duemilanove w/ATmega328 as the board!
Now try to upload the File->Examples->Basics->Blink example sketch. If successful, the Red LED on the Menta should blink