Also, from your description of that rally event it sounds like a "Rally Cross" - similar to autocross but run on dirt instead of parking lots, with cones to mark out a course. Try Googling or searching for local RallyX events to talk to some novice drivers first hand.
The S, SE etc refers to the trim level of the Focus. Basically, more letters = more options. A dealer would be able to explain everything. Any Focus through 2007 MY is available in 3- or 5-door hatchback, sedan, or station wagon. Current models have a 2.0L Duratec engine exclusively, except for a sportier sedan called the ST trim level that has a 2.3L Duratec (sourced from Mazda). Some 2.3L Duratecs can be found in 2003-2004 MY hatchbacks; most pre-2005 Foci employ the 2.0L Zetec. The SVT Focus built between 2002-2004 has a very nicely factory-modified 2.0L Zetec.
Hopefully that helps and answers some questions... After writing all that I can see it gets a little confusing! You can see that the forums here are seperated into Zetec and Duratec performance boards so you can explore potential of the two engines. There's also a board specifically for SVTs as well as a Racing board - look into that one for rally/rallyX info and events.
Have fun and Welcome!
An afterthought: FocusSport, a popular source for Focus aftermarket, makes a turbo charger for Duratec applications (capable of producing 260+ whp in a D23). There are also one or two offerings for turbo charging a Zetec in development by various fab shops/tuners, and multiple superchargers are available for Zetec (ProCharger and JacksonRacing are examples). This could make a potent racecar for a low price. However as previously mentioned I've also always heard that a used rally car is the best option to use to get into the sport. I would guess that high-power FWD would require a great deal of skill to rally race competitively.
2005 InfraRed ST FS Stage 2 (Totaled)
2008 BlackMica Mazdaspeed3 GT