php +javascript +form

[MarcustheWinter]

if ($verzendbutton != "send" || valid_name($name)) {

echo "<form action=\"$PHP_SELF\" method=\"post\">";
?>
<input name="name" type="text" value="<?php echo $name ?>" size="15" maxlength="30"><?php
if ($verzendbutton && !valid_name($name)) {
echo "<font color=\"red\"size=\"1\"><br/>Vul hier uw achternaam correct in!</font>";
}
?>
<input type="submit" value="send" name="verzendbutton">
<input type="reset" value="wissen" name="wissen">
</table>
</form>
<?php
} else {
$mailadres = "[e-mail]";
$to = "[e-mail]";
$message ="\nname: ".$name;
mail($to, "order:", $message, "From: $mailadres");
echo "<br/>Thanks".$name."<br/>You will here from us soon"; }

well... that was my code... so far so go.. it works...
now, my question is: just One easy javascript alert().
When someone has forgotten to fill in my form RIGHT, it will not be send indeed, but a javascript alert will make the difference...
then they certainly gonna look were they didn't fill the form correctly.
(After spending my whole Easter on it I give up; especially because I thought it would be easy.)

I made this:

function js_alert($bericht)
{ if ($verzendbutton != "send")
return;
echo (
"\n<SCRIPT LANGUAGE='JavaScript'>\n" .
" <!-- \n" .
" alert (\"$bericht\");\n" .
" // --> \n" .
"</SCRIPT>\n"
);
}

// call function
js_alert("You filled in wrong!"); 

i combined it but now I allready got an alert when they get on my form.php
I only want an window.alert when they filled my form incorrect or not at all...
Who can help me?
Thanks.

[weevil]

You need to add something like this to your form tag

onSubmit="return validate_form(this)"

and create your function in javascript inside the script tag.

[MarcustheWinter]

Well, were shall I put it then, when you look at my script above?
What i made wasn't that bad, was it?

Php does the validation and just one lausy Javascript alert to do the warning... Well... It ain't my stuff...yet.

Could someone please ad more complete answers?