You can do this one of two ways edit your controls in Mirc Options\Dcc and Mirc Options\Dcc\folders as far as accepting files from others
now the other you can find in the help section by typing
/sreq [+m|-m] [ask | auto | ignore]
This is the command line equivalent of setting the DCC Send request radio buttons in the dcc options dialog (see /creq above). The +m|-m switch turns the minimize setting on|off.
Intelligence: It's better to ask a stupid question, then to prove it by not asking....