You find the pb folder inside the game folder on your server.You do not add any folder <_< But inside your pb folder you will likely find a file called pbsv.cfg which you want to edit using your notepad or wordpad (download the file if needed and upload it after you have editted the file when needed, if it is a remote server).
Once you opened the pbsv.cfg file, scroll down and add a new line to read:
pb_sv_load servermsg.cfg
Save and close the file and put it back into your pb folder.
Now create a new file (called: servermsg.cfg) using your notepad or wordpad and add the following content:
//================================================================================
// Added by hugin - 2007
// Task setup for PunkBuster
//================================================================================
// 30 sec intervals - Remember: pb_sv_task 460 + 30 (Interval value) = 490, and so on
// Task setup for PunkBuster
pb_sv_task 10 490 "say message 1"
pb_sv_task 40 490 "say message 2"
pb_sv_task 70 490 "say message 3"
pb_sv_task 100 490 "say message 4"
pb_sv_task 130 490 "say message 5"
pb_sv_task 160 490 "say message 6"
pb_sv_task 190 490 "say message 7"
pb_sv_task 220 490 "say message 8"
pb_sv_task 250 490 "say message 9"
pb_sv_task 280 490 "say message 10"
pb_sv_task 310 490 "say message 11"
pb_sv_task 340 490 "say message 12"
pb_sv_task 370 490 "say message 13"
pb_sv_task 400 490 "say message 14"
pb_sv_task 430 490 "say message 15"
pb_sv_task 460 490 "say message 16"
//================================================================================Edit the content to your liking and once finished, save and close the file and put it into your pb folder.Then do pb_sv_restart in console or thru your rcon tool