It wouldn’t be untrue to say that the Prep’s were involved in Gary’s plans, but no more so than any of the other Cliques. Earlier in the Plot, Tad is obviously impressed that you managed to actually defeat Russell, and so, seems to want to give you a chance to prove yourself worthy of corporation with the Preps (The Eggs Mission) So as you know, you meet him along with Chad and Parker then go off to buy some eggs to throw at Hattrick Manor, but during that time Gary obviously meets with Tad and feeds him a load of trash about you calling him inbred and causing him to turn on you when you return with the eggs, which is generally the start of your war with the Preps.
From this point onwards during the earlier stages of the story, Tad does seem to have particular hinted connections with Gary, using taunts such as “Well, if it isn’t Gary’s errand boy!” and “You think I can’t cream you? Gary told me you can’t fight!” later in the game though, when you’ve won the Prep’s respect, it’s hinted that Tad actually now rejects Gary.
The actual quote you heard was “Wait until Gary hears what I’m going to tell him about Jimmy!” I might be wrong, but to me, this sounds like Tad is looking forward to telling Gary how much more successful and popular Jimmy is now within the school, probably making Gary flip his lid, which Tad may find amusing or whatever...
Overall, Gary has equal if not more affiliation with the other cliques than the Preps, urging Johnny and the Greasers to harass Cornelius in order to get information on Algie’s whereabouts, promising Earnest some sort of domination during the final chapter. His connections to the Preps seems to be actually quite narrow, he has no association with Derby throughout the entire plot, and only causes the Preps to turn on you a second time by encouraging the drop-outs to steal their trophies. Even during the last mission, Derby still seems to have minimum participation with Gary’s plan, he just lounges in Harrington House, enjoying watching riots. The only Prep he really seemed to have connections with was Tad, and as I mentioned, that quickly seemed to be terminated at the end of chapter two.
Also, just to clear things up, it is actually quite heavily suggested that Gary is most defiantly NOT rich. Miss Abby (the old woman in New Coventry with the blue/cyan clothes) talks about knowing Gary’s parents well, especially his mother who is also hinted to be a resident of New Coventry.
I understand what you mean though; I’m always picking up on students talking about Jimmy behind his back:
Bo:
“Freakin’ Hopkins man...”
“Hopkins is a cheat and a rat, and he’s gonna get what’s coming to him!”
Gord:
“Derby says Jimmy Hopkin’s is the biggest disappointment since universal suffrage!”
“I hear Jimmy is going to do something amazing this year, not quite sure what it is yet, sure to be impressive though!”
Damon:
“I heard Jimmy burned down the Gym, ‘cause they were gonna start making his Stink-Butt take showers after Gym-Class!”
“I don’t care if it wasn’t Jimmy, I STILL hate that Punk!”
Kirby:
“I think Hopkin’s was the one who burned down our Gym!”
“Word is, Hopkin’s is trying to get everyone to fight each other...”
“Word is, the new kid thinks he can rule Bullworth by next spring!”
Ethan:
“I’m really starting to like that new kid, he’s got some real moves. All he needs now is for me to teach him some techniques, and he could be like ... a destroyer, man!” (...or something along the lines of that)
“That new guy totally smoked those Preps, he must have some real training!”
Tad:
“I know Jimmy is doing SOMETHING for Edna!”
“Wait until Gary, hears what I’m going to tell him about Jimmy!”
"That weasel Jimmy ... is more than he seems" (I don't really know why, but Tad seems to pause in the middle of saying this...)
Davis:
“Jimmy Hopkins thinks he’s smart but he really isn’t, he’s just a loser who pretends to run this school!”
Trent:
“I can’t believe that Hopkins snot did Russell in!!”
Parker:
“Derby says not to mingle with the new kid as he’s VERY low class!”
“The greasers broke into the Gym and stole all the trophies, frankly doesn’t surprise me at all!” (Well at least he doesn’t think it was you...)
Juri:
“Jimmy is the toughest, that is why he rules...”
“Jimmy was a fool, that is why he no longer rules...”
Ray:
"I think if me and Jimmy were friends, he wouldn't act out all the time, and like, burn down the Gym!"
Norton:
I can’t remember exactly what he says but its something about settling a score with you “real soon”...
Dan:
“So that new kid Jimmy Hopkins thinks he’s tough does he?”
“Who does that Jimmy Hopkins think he is anyways?”
Wade:
“That new kid looks like trouble, I heard he’s really bad-ass!”
“I just found out the Preps are gonna ‘Prep’ the new guy, haha, sucker!”
“Gary’s been telling me all sorts of crazy things about Hopkins!”
“I hear Hopkins’s been (laughing at all of us?) in his room!”
Omar:
“I hear that Gary’s got some big surprise for some kid named Jimmy!”
New Coventry motel-owner (Brown suit and Eastern-European accent):
“Chimmy Hopkins is fantastic! I think he might be my illegitimate son!”
Peanut:
“I think that hero Jimmy is a real (patch?)”
“I’ve got a score to settle with that hero, Jimmy!”
“How’d Jimmy turn out so good, so fast?”
Tom:
“Some new guy’s tryin’ to get serious with Russell, haha!”
“That new kid’s ben hassling the preps a lot lately, that’s cool, I hate the preps!”
“I guess, Hopkin’s isn’t so bad after all!”
“I was right about that Hopkins, he’s nothing but a little punk!”
Chad:
“That new kid wrecked the class system we worked SO hard to build!”
This is one of the things I don’t like about the game, even when you’ve completed the story line and everyone’s friends again, half the students still obviously hate your guts...