Phew .. finally also added searching "Threads" and "Members" using forum search
But that was a lot of effort ..
shabbir should have told me how to submit a search using search.php and memberlist.php.
I had to spend a
LOOOOOONG time studying their behaviour.
But after studying the page-source
+ some experiments with the forum + a bit of intuition, I made it.
Phew .. hard work !