Khaled's example will actually do just that, return a random line from the file.
$read by default evaluates the line as though it was a line of code (if the line contains "$me", it will be evaluated to your nickname, this can be and is often the case, not desired).
$read will also use the first line in the file if it's a number, to speed up processing, where that number should indicate the number of line in the file, this is also usually not desired (an old feature), when the file's content is not known in advance.
The 'n' switch will prevent the evaluation, and the 't' switch will prevent mIRC from taking the first line as the the total number of lines in the file, if it's a number.
Check the help file for more information by typing in mIRC /help $read
$read(myfile.txt,tn) is probably what you are looking for
