If you're wanting the user to upload multiple files, you'll need to use a <input type="file" name="f1"> tag for each file you want to upload. On the server side, you'll then need to check each input variable to see if it's a non-zero length and then process with <cffile action="upload"...>. I've checked and I don't believe there is a way to use one <input> to handle multiple files though.
Good luck,
GJ