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Here is a howto on configuring a serial port as a console device. This will allow you to login and and execute commands. You can use any terminal program ie Hyperterminal in windows or minicom in linux are the most common.
There are some utilities i.e. rz, sz (receive and send using zmodem protocol) that you can use via hyperterminal or minicom to send/receive files. You initiate the transfer on the server then use the built in transfer routine on the client application. There are also xmodem and ymodem transfer apps too.