In addition to adding the lines to /etc/network/interfacesyou must also restart the network interfaces (/etc/init.d/networking restart) probably because of the order in which the network and pcmcia interfaces are configured.
This later step is probably not necessary with the kernel pcmcia support of the 2.4.x series kernels, but since the bootdisks will use the 2.2.x series, I guess it is.
TRS