I'm a little late with this reply but I'd like to clear some stuff up.
An easy way to tell a WRX and RS apart on the 2002 models is that the RS won't have a hood scoop and of course the badging.
On previous models, it's real easy: there was no WRX offered. This is the WRX's 1st year in the US and Canada.
As for the STI or P1 (?) neither are offered OR will be offered in the US for a long time if at all. Subaru is testing the waters with the current WRX to see how well they sell before bringing over the STI. Currently there are NO plans for it, but possibly in a couple of years.
FWIW, I own a 2002 WRX and I ran a 14.5 @ 92.7mph, 100% bone stock, 1300 miles, 70 degree weather, 250lb driver, 1/2 tank of gas, and my 1st time to the track in this car.
A stock Mustang driver shouldn't take these cars lightly. A couple of mods and 13's won't be a problem.
Just a warning....
------------------
Chris
1989 Mustang LX
2002 Impreza WRX