Detecting LAN, please help

Hello,

I have a html document that is browsed as a local file in a PC. The
document displays an image stored in the local disk. What I really
want is for the document to fetch an image from a remote URL if the PC
is connected to a local area network. If not, the local image should
be displayed. I have two questions in this regard.

1. Could you help me write a javascript that can figure out if LAN is
available and depending on that display the correct image (from remote
URL or local URL)?

2. When a remote image is being loaded, can the process be aborted
after a fixed amount of time and the local image displayed? If so,
how?

Thanks in advance.

Sooby
(thermo.sdsu.edu)