When I bought the car, it had P215/45 R17, but I'm trying to purchase some new ones, and the guy is telling me that its suppose to have P225/45 R17.. Whats the difference anyway?

go to tirerack.com put in your car and it'll tell ya what you need. The differance is the width of your tire in millimeters 215 or 225 not a real big differance

Go to http://www.tirerack.com/ and use their calculator to see what tire rim combinations fit your RSX-S

205/55/16

the difference is...milage, rubbing, braking, etc.
read the side of your tire, it says the size on there...(it's also on the plaque on your driver door.)
buy some Bridgestone Potenza RE960AS
(they no longer make pole pos 3's)