D'oh!
Now I understand you. I must be blind...

Thanks DarkReaper!
It works, because the filed-names in both tables were nearly the same... I Updated the hack. The Changes were small, but now it is better.
Update:
First go to the New Menu. Sort Preselection.
Disable all Columns. (You not disable rows, if you are shure, the they are in both tables the same! e.g. title)
Opel admin/forum.php:
Search for:
PHP Code:
$sortinfos=$DB_site->query("describe forum");
It appears two times, replace both with:
PHP Code:
$sortinfos=$DB_site->query("describe thread");
Now you can reset you Sort Preselection! You will see, that the List is smaller.
That's all!