Not sure what you have, but Linksys works in 1 of 4 modes.
Access Point Mode (Default)
Wireless Repeater Mode
Access Point Client Mode
Wireless Bridge Mode.
Set it to Wireless Repeater Mode and it will just "repeat" the signal of your first Access Point. To set it to Wireless Repeater Mode, you will need to know the MAC address of your first Access Point that you want to "repeat".
Not sure what options other vendors offer, but it's probably similar.