Ralley_T,
It's been a while since I inserted my Sirius antena behind the pillar cover, but you are correct, there are plastic retainers (3) holding the pillar covers onto the wiindshield posts. Open your door (whichever side) face the pillar cover, reach up on the door seal side and grab the pillar cover at the top. Pull it out and away from the door seal. Once it clears the door seal reach up to the top of the pillar cover opening to the pillar and slide your fingers down inito the top and start gently pulling (more or less to the oposite side of the car) and the top one will pop loose, continue moving from the door seal side back to gently tugging until they all three let loose.
I just went outside on my Tracker and did this (to make sure I was still "trackin" on the technique)... it popped right off! The actual pillar cover has slots in it, then the "clips" (in the case of the Tracker) are red tits that insert into the slots on the pllar cover. It's kinda like those damned rear cover in the back of the hatch (yeah, I've trashed a couple of those also!), but in this case those red tits "pop" into a hole in the windshiled pillar to secure the pillar covers.
FYI, on removing the front door sills, after you remove the three plastic clips, you have to lift up and push in on the cover as you lift it or you will break one or more of the plastic tangs that are seated into the flat part of the door sill. The tangs hold the flat part snug.