I read something like this sa miragepilipinas. He had a 2gb card and winterpine gave him a link to a "lite" version of the updated maps that will work on his 2GB card.
But I think getting it replaced at winterpine is a better (and long-term) solution. IIRC it costs about 500 pesos to change to 4GB.
Sir bago mo gawin back up mo yong files ng sd card[gps]para ano man mang yari meron ka pa files.minsan kasi destorted sya kahit succesful ang downloading.