If connection is only rarely required and only for file transfers, why not use a USB memory-stick? Capacities up to 2 GB are now available, and the price is less than a PCMCIA network card!
Take it a bit further, and get a large external USB hard disk and solve backup AND file transfer in one go!
Next you'll want to install a network-attached storage device - oh hang on, there isn't a network!
SD