Ethernet and USB have considerably-higher program code and component
overhead than RS-232 and most all microcontrollers already have an RS-232
port cast in their silicon that literally comes for free.

The cable listed in the message below is a Cisco serial console cable and
isn't useful for anything else.

Here are a few of a number of devices that will convert serial RS-232 to
Ethernet:

http://www.netburner.com/products/serial_to_ethernet/sbl2e.html

These modules could give your mount an Ethernet interface, as well as it's
own web status and control interface:

http://www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/P
roductID/710/List/1/Default.aspx?SortField=UnitCost,ProductName

http://www.netburner.com/pink/

Serious programming would be required for either module, as well as on the
far end computer.

A box with multiple serial ports on one side (often up to 32) and a single
Ethernet connector upstream is commonly called a Terminal Server. We use
them quite frequently in the big observatories to connect a multitude of
specialized-task microcontrollers to a control PC on the observatory
network.

http://en.wikipedia.org/wiki/Terminal_server

I hope this helps.

Christopher Erickson
Consulting Engineer
Summit Kinetics
Waikoloa, HI 96738
www.summitkinetics.com