I have a Cisco/Linksys WRT-54G wireless router and 2 Airport Extremes (the small ones that plug directly into the wall). Is it possible to extend the network from the router using these two AEs? I have a DVD player and Ext HD plugged into the router too..

The Cisco/Linksys WRT-54G was one of the very few routers said to be compatible with Apple's implementation of WDS (Wireless Distribution System) settings.

The info that I have on file indicates that only the WRT-54G versions 4 and under were compatible, so that would be one bridge to cross.

Even if you find that your Cisco/Linksys might be the right version, Apple never published instructions on how to configure the Express devices with other manufactures, so users were left to their own devices to try to figure out how to get things working. Apple's instructions to connect to other Apple devices are in the link below:

WDS network

If you were hoping to use 2 Express devices in this type of configuration...even if it works...the bandwidth penalties will be extremely severe.

The first Express drops the bandwidth (and speed) on the entire network in half and the second halves everything again. So, the result, in effect would be a "g" wireless network running at 25% speed. Few users would consider installing this type of network.

At this point, it becomes one of those things where the fact that you might be able to do something does not mean that there would be much value in doing so. But, it is your decision to decide if you want to try to proceed.

I don't actually have to use 2 Airport Extremes.

If you can get a wired Ethernet connection to one of the AirPort Extremes, that would really help the performance and speed of the network.

That would take the Cisco/Linksys product out of the network entirely, but it would be a way to extend the network.

You would have a "main" AirPort and a "remote" AirPort in this type of setup.