you're obviously just getting started. do a search of these forums. in addition,
www.saem.org under residency catalog has a lot of information.
i look back at how clueless i was when i first applied so let me give you some basics.
EM programs are 3 or 4 years long. they are refered to as PGY 1-3, 1-4, or 2-4. there are a lot more 3 year programs. 4 year programs are either straight through (1-4) or like cook county (PGY 2-4) which require a prelim/transitional year prior to 3 years of EM training. so no, cook county and all other programs refered to as PGY 2-4, are only 4 years total.
when you apply for residency, you match into your PGY-2 spot at the same time you match into your prelim/transitional (aka PGY-1 yaer). so no, it does not increase your chances of matching.
whether you want a 3 or 4 year program depends on what you are looking for, whether you like the program, etc, etc. the utility of the 4th year has been debated extensively on these forums as well as on saem.
good luck. read the faq's. i think the format is a little rough but contains lots of good information.