Im struggling trying to get $username to show up

[powerful_rogue]

Hi,
Im still learning the ropes, so I thought I would take quite an easy hack and re-code differently.

This is what the code was orginally

$title = "This just in: " . $username . " has just joined the forum!";

Im trying to get it so that you can enter the title via the acp rather then having to edit the product.

This is what ive got -

$title = $vbulletin->options['ntur_title'];

$threaddm->do_set('title', $title);

<setting varname="ntur_title" displayorder="20">
<datatype>free</datatype>
<optioncode>textarea</optioncode>
<defaultvalue>Welcome $username</defaultvalue>
</setting>

However when the thread gets posted, the title shows up as "Welcome $username" - rather then the username of the person that has just registered.

Im getting there on the other parts, however seem to have hit a stumbling block on this!

Any help greatly appreciated!