I don't own one of these rigs, but I have a lot of experience doing mods to the 703N. There isn't an SD card if it's a stock device, but there are probably ways to get a copy of the firmware if you want to play around with it (of course, you might break it too, so be careful). Lots of info here:
http://wiki.openwrt.org/toh/tp-link/tl-wr703nPost the hash file of the root password, I wouldn't think it'd be too hard to decrypt.
I can't ssh the controller, so I can't extract the file. Maybe there is an SDCard inside the controller. Didn't think about that. Will check.