Replacement setup for '92 G20

I was just originally planning on replacing the stock AM/FM Tape Deck with this one:

Pioneer DEH-P4700MP CD/MP3/WMA Player
http://www.pioneerelectronics.com/pna/product/detail/0,,2076_4039_150454051,00.html

I JUST got this car and I was a little shocked when I turned on the radio for the first time & I got cracklin' & popping noises coming from the rear speakers. I now want to replace the rear speakers, but I don't wanna dish out too much money. This car is just a temporary car & I don't wanna put too much money into it. I just wanna replace the rear speakers so that they don't crackle. I was able to find some pretty cheap ones to replace the rear speakers. I was able to find these on Overstock.com

SDAT SD-604 200W Car Speaker System (Pair) - $18.99
http://www.overstock.com/cgi-bin/d2.cgi?page=proframe&prod_id=1415163

& then I stumbled across these speakers that would fit in the front:

SDAT SD-464 200W 4-way Car Speaker System (Pair) - $15.99
http://www.overstock.com/cgi-bin/d2.cgi?page=proframe&prod_id=1415187

The main questions I have about this setup are:

How difficult is it to replace the front speakers?
How difficult is it to replace the rear speakers?
Will I be required to run new speaker wire for these speakers?
Will I be required to buy a new amp to power these speakers?

Any help/comments/suggestions regarding this would be MUCH appreciated :grinyes: . Thanks in advance!

I just changed my back speakers right now. It isn't too difficult now that I know how to do it but it does take a llot of searching for screws and clips to take out. You have to take out the whole back seat.