If you know the wysiwyg editor well, it is easy to implement it.
Just modify this (perhaps).
line 423 of admin/index.php
// content body
$spaw_flag = false ;
if( ! empty( $_GET['usespaw'] ) ) {
// SPAW Config
include XOOPS_ROOT_PATH.'/common/spaw/spaw_control.class.php' ;
if( check_browser_can_use_spaw() ) {
ob_start() ;
$sw = new SPAW_Wysiwyg( 'message' , $message ) ;
$sw->show() ;
$form->addElement( new XoopsFormLabel( _TC_CONTENT , ob_get_contents() ) ) ;
ob_end_clean() ;
$spaw_flag = true ;
}
}