Cleaned it up some try this i didn't test it, just eyeballed it. But the gist of the changes were that to connect strings together you need to use '.' not '+'. Also check out some of the functions such as is_file() or is_dir().
<?
//set variables
$timeofyear = date( "M:Y");
$fn = "../texts/".$timeofyear.".txt";
$content = $_POST['content'];
//check file existence
if(is_file($fn)){
$fp = fopen($fn,"w");
fputs($fp,$content);
fclose($fp) or die ("Error closing file!");
}
?>
<form action="comments.php" method="post" class="style6">
<textarea name="content" cols="100" rows="20" class="style12" id="textarea1">
<?
//were you trying to get rid of spacing in filename? If so that's what below does.
print str_replace(" ", "", $fn);
?>
</textarea>
<input name="submit2" type="submit" class="style13" value="Add Comments" /></form>