I ran into this today installing from the DVD image and tried to work around it with

cp /cdrom/firmware/*  /target/lib/firmware/ 
chroot /target
dpkg -i /lib/firmware/firmware-realtek*.deb

then tried to get the installer to see the wireless interface. It wouldn't do it, so I just finished the install.

On reboot, I found that I needed to install wicd, so I plugged in a wire, added wicd, and the wireless interface is working.