I'm sure I read somewhere that one way of doing it is to burn your game saves onto cd, put the cd in the Dreamcast then copy them to your memory card. Although I'm sure you'll need to first have some kinda program running on the Dreamcast to do the copying.
Sorry it's not too specific, but there must be a website out there that'll be more help.
Old geeks don't die, we just incur a fatal exception!