Hi,
If both units are identical (model, IOS version), then you can probably copy the config from the existing AP to the new one. The possible config that might conflict between them are:
a. Physical IP Address - each need unique IP
b. Radio Channel - best to configure both to use dedicated/different channel (choose either channel 1, 6 or 11) to avoid overlapping channel.
You can maintain the SSID, WEP key (if any) and other config.
BTW, do you use DHCP or static IP for the client? DHCP is enable by default to allow clients to get an IP.
Rgds,
AK