Это не в .htaccess прописывается, а в самом скрипте загрузки.
вот код на ПХП. переделаешь под себя и все чики-пики:) Бай.

<?php
/*
* File uploads made easy
*/
                        
$my_max_file_size     = "1073741824";     # in bytes
$image_max_width    = "1600";     # in pixels
$image_max_height    = "1600";    # in pixels
$the_path        = "/usr/www";

$registered_types = array(
    "application/x-gzip-compressed"     => ".tar.gz, .tgz",
    "application/x-zip-compressed"         => ".zip",
    "application/x-tar"            => ".tar",
    "text/plain"                => ".html, .php, .txt, .inc (etc)",
    "image/bmp"                 => ".bmp, .ico",
    "image/gif"                 => ".gif",
    "image/pjpeg"                => ".jpg, .jpeg",
    "image/jpeg"                => ".jpg, .jpeg",
    "application/x-shockwave-flash"     => ".swf",
    "application/msword"            => ".doc",
    "application/vnd.ms-excel"        => ".xls",
    "application/octet-stream"        => ".exe, .fla (etc)"
); # these are only a few examples, you can add as many as you like

$allowed_types = array("application/msword","application/vnd.ms-excel");

///////////////////////////////////////////////
function form($error=false) {
global $PHP_SELF,$my_max_file_size;
    if ($error) print $error . "<br><br>";
    
    print "\n<form ENCTYPE=\"multipart/form-data\"  action=\"" . $PHP_SELF . "\" method=\"post\">";
    print "\n<INPUT TYPE=\"hidden\" name=\"MAX_FILE_SIZE\" value=\"" . $my_max_file_size . "\">";
    print "\n<INPUT TYPE=\"hidden\" name=\"task\" value=\"upload\">";
    print "\n<P>Upload a file";

// Real max file size is ($my_max_file_size / 1024) - We are trying to put pepople off adding bigger files

    print "\n<BR>NOTE: Max file size is " . 200 . "KB";
    print "\n<br><INPUT NAME=\"the_file\" TYPE=\"file\" SIZE=\"35\"><br>";
    print "\n<input type=\"submit\" Value=\"Upload\">";
    print "\n</form>";

} # END form

if (!ereg("^4",phpversion())) {
    function in_array($needle,$haystack) { # we have this function in PHP4, so for you PHP3 people
        for ($i=0; $i < count($haystack); $i++) {
            if ($haystack[$i] == $needle) {    
                return true;
            }
        }
    }
}
//////////////////////////////////////////////////////

function validate_upload($the_file) {

global $my_max_file_size, $image_max_width, $image_max_height,$allowed_types,$the_file_type,$registered_types;
    
$start_error = "\n<b>Error:</b>\n<ul>";
    
    if ($the_file == "none") { # do we even have a file?
    
        $error .= "\n<li>Вы не выбрали ни какого файла!</li>";
    
    } else { # check if we are allowed to upload this file_type
    
        if (!in_array($the_file_type,$allowed_types)) {
            $error .= "\n<li>Тип файла, который Вы хотите закачать, ".
                "является недопустимым, Вы можите закачитавь только файлы типов:\n<ul>";
            while ($type = current($allowed_types)) {
                $error .= "\n<li>" . $registered_types[$type] . " (" . $type . ")</li>";
                next($allowed_types);
            }
            $error .= "\n</ul>";
        }
    
        if (ereg("image",$the_file_type) && (in_array($the_file_type,$allowed_types))) {
        
            $size = GetImageSize($the_file);
            list($foo,$width,$bar,$height) = explode("\"",$size[3]);
    
            if ($width > $image_max_width) {
                $error .= "\n<li>Your image should be no wider than " .
                    $image_max_width . " Pixels</li>";
            }
            
            if ($height > $image_max_height) {    
                $error .= "\n<li>Your image should be no higher than " .
                    $image_max_height . " Pixels</li>";
            }
        
        }
        
        if ($error) {
            $error = $start_error . $error . "\n</ul>";
            return $error;
        } else {
            return false;
        }
    }
} # END validate_upload
//////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////
function upload($the_file) {
global $the_path,$the_file_name;
    
    $error = validate_upload($the_file);
    if ($error) {
        form($error);
    } else { # cool, we can continue
//do_insert();
        if (!@move_uploaded_file($the_file, $the_path . "/" . $the_file_name)) {
            form("\n<b>There was an error, check the path to and ".
            "the permissions for the upload directory</b>");
        } else {
//            list_files();
//            form();
        }
    }
} # END upload
//////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////

switch($task) {
    case 'upload':
        upload($the_file);
    break;
    default:
        form();
}

?>