The IOS (Firmware) of the 1841 is not compatible with Cisco 2900. So i think you want the configuration of the Cisco 1841.
You can copy the running-config to a TFTP server (copy running-config tftp), or copy the running-config to usb stick (copy running-config usbflash0).
To put the config on the Cisco 2900. You can copy the configuartion file from the TFTP server of usb stick. (Copy tftp running-config) (Copy usbflash0 running-config)