To be honest, I am not sure if that router supports FTP. I am quite sure the WL-500W and WL-700gE do. You might want to head over to the ASUS official forums, and check out the WL-500g forum to post the same question there.
If you do find a router that will support FTP, it will still be a little tricky setting it up. You might need to set up a DynDNS.org account to set up a domain that links directly to your routers/computers IP address. I've done this before, but don't recall the exact process. It took about an hour to figure out though.