Hi all, I need some quick expert help. My buddy has a duemilanove that has a burnt out FT232RL. Everything works, except of course no usb connection. I have a cheapo RS232 usb adapter, and I'd like to program using it. Can I just hookup tx and rx, power it up, and go? He needs this for engineering class, so we have to think of something asap. Whats the best way to go about this?
Can I just hookup tx and rx, power it up, and go?
No the output from your adaptor is RS232, these are +/- 12 V signals, these need to be converted into 0V +5v TTL signals with a logic inversion. Your best bet is to run it through a chip like a MAX202, that will give you signals you can feed straight into arduino. You also need the DTR coupling through a capacitor to the reset line to give you the auto reset function.
ya you can definitely program that board.. But all you will need is MAX232 that is logic converter and use schematic given by arduino..
arduino-duemilanove-schematic.pdf
hence connect Tx, Rx and also RESET pins of your serial port with arduino.. and from above schematic see how the RESET pin has to be connected with RTS and DTR. This will autoreset your controller before burning code on that.
and rx & tx pins have to be connected after level translation using max232. see the connection from below diagram.
goo.gl/vkNB
and ya you don't need to translate level on RTS or DTR pins.. It will work.. 
and ya you don't need to translate level on RTS or DTR pins.. It will work
Yes it will work and it will also subject the reset pin to voltages above the absolute stress levels. The data sheet says about absolute stress levels:-
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage
to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
and ya you don't need to translate level on RTS or DTR pins.. It will work
ya thats true, no offence about it... but here in our case the RESET pin is active LOW logic. N even RS232 standard for PC serial port specifies that it can vary in 25V range from +15 to -15. But here DTR pin is connected to RESET pin through a capacitor. So it works at protection anyways and same way there is a big resistance at RTS pin.
So thats why here on this 2 pins no need of level conversion... I have already tested and i've been using it from last 6 months... 