As it turned out the router already had a version of DD-WRT already installed on it. At this thread below note 1
I learned the general procedure of upgrading the firmware.
I searched eBay for a Linksys WRT54G V1.0 with DD-WRT installed on it. I found a vendor
who was very helpful and even suggested a build of firmware to use and provided me with tutorials on how to configure the firmware
You were right about using only one antenna. Under the "Wireless" > "Advanced Settings" you can choose which antenna you want to use. You can even choose one antenna for receiving and the other for transmitting.
Do you think you could attach two parabolic antennas pointed in different directions to make a really long distance repeater?
I've heard that there is a lot of power loss in the cables that attach to the antennas. I'm thinking about mounting the router right next to the focal point of the antenna and just using short adapters to connect it. Do you see anything wrong with that?