when you DCC a file to someone, look in the DCC screen for a checkbox labeled Fill Spaces. Once you UNcheck this box, then successfully send a file, the setting is remembered and from then on, for all files you send to others, spaces will not be replaced with underscores. You can also use this little snippet I made a while back, to remove underscores from all files you receive:

Code:
on *:filercvd:*.*: {
  .rename " $+ $filename $+ " " $+ $nofile($filename) $+ $replace($nopath($filename),_,$chr(32)) $+ "
}


Hope this helps.

-Venoman