welcome man, im new too...
check out
Crutchfield: LCD TV, Car Audio, Home Theater, Speakers, Plasma TV
they have incredible amounts of decks, speakers, subs, amps...the works, and its not half bad priced either.
as for a deck, check out a kenwood or a alpine if you want to turn some heads on looks...and for dealing with the rear speakers, just disconnect your battery and take it very slow and examine everything. just take a few hours out of your day and just explore and try to find a way in. it could be as easy as taking off a cover, or you may have to take out carpet
if you do need to take out carpet, and its the carpet molded to form fit your car, just get a heat gun and warm it up and it will be nice and easy to deal with. when your ready to replace it, just re-form fit it