PHP Code:
// Make the filename safe for the OS (remove anything but letters, numbers, ., _, and -)
$file = preg_replace ('/[^a-zA-Z0-9\._-]/', '', $_POST['file']);
$cont = '<tr><td><b>'.$_POST['event'].'</b></td></tr><tr><td>'.$_POST['date'].'</td></tr><tr><td>'.$_POST['time'].'</td></tr><tr><td style="padding-bottom: 10px;">"'.$_POST['description'].'"</td> </tr><br />';
$f = fopen ($file, 'w');
fputs ($f, $cont);
fclose ($f);
That's very simplistic, you need to sanitize all user input before using it, but it'll give you an idea of how to go about it. Note that I'm using the $_POST supervariable to access the data, change this if you're submitting the form via GET.