Erm, I've never used 5.61 and I don't know if you can. Have you tried the usual:ALT+O > IRC > Options
and see if the "Hide ping! pong? event" box is there, and if so, check it.
It is possible of course that it simply doesn't exist in that version, check out http://www.mirc.co.uk/versions.txt
and see if you can see any related additions in future versions which means it wasn't present in previous ones. mIRC has developed leaps and bounds since back then.
Of course, the thing that I suggest the most is upgrade to version 6.12
and have all your problems solved! If the Trivia bot doesn't work under that version, there are plenty (by plenty i mean lots and lots!) of Trivia scripts/bots out there from sites such as mircscripts.org