This is what I do:
1.) Change .htaccess to
ErrorDocument 404 /redscript.php
DirectoryIndex redscript.php index.php index.html index.htm
2.) Rename index.php til redscript.php
3.) Make a new file called index.html with this form:
<table class="border" width="320" border="0" cellspacing="0" cellpadding="0" bgcolor="#f5f5f5">
<tr>
<td bgcolor="#f5f5f5">
<form method="post" action="myred/register.php?do=check">
<div align="center">
<br>
http://<input type="text" name="domainname" size="20" maxlength="63" value="">.d4a.com <input src="http://www.d4a.com/img/btn_check.gif" name="check" type="image" alt="Check if your url forwarding is available" align="absmiddle"><br>
Example:
http://<b>YourName</b>.d4a.com<br>
</div>
</form>
</td>
</tr>
</table>
4.) Change settings for admin to use index.html as start page