Can I use an older Airport Express to expand network using a new Airport Express?
I've got an older Airport Express, and wanted to swap it for a newer version and use the older one to expand the range in our home. Can this be done?
By "older" are you referring to the 802.11g AirPort Express (model A1084)? If so, then you will not be able to use it to extend the newer Express with a wireless connection between them.
However, you could use it in a roaming network configuration, which would require the base stations to be interconnected by Ethernet.