Help - Getting Certain NavTabs Highlighted

[ARNK]

So the ID is 74 and the tab is tab_mja2_349. Seems pretty straight forward but I'm missing something Lynne.

So, the code is: if (intval($_GET['r']) == 74) $root = 'tab_this_349';

I just go to create New Plugin. Then find the hook location... plugin the code and set it to active right? But this doesn't work. I'll try to find that section in the manual... but appreciate your help so far.