Installing new headunit and 6x9s

[LiquidCell]

Ok, I am 17 and MAY be getting my moms Honda Civic 2000 SE for when I move out after grade 12 (moving to fathers place for college) and so far the only new speakers I have put in the car are a pair of CDT Audio CL-6X in the front door panels, sound somewhat nicer, but what I really need to get better sound is a new head unit. I was looking at this:

http://www.futureshop.ca/catalog/pro...CBBCA75FBB6E17

Anywho, I was just wondering, how would I go about installing my OWN head unit if I bought the JVC one I like more located here:

http://www.outerlimitsaudio.com/prod...ProductID=4667

Also, I have a pair of Pioneer G6910 speakers that are 6x9 that I bought off ebay for around $35.00 USD Shipped. I was trying to put them in to replace the rears with a good friend of mine and the plastic covering over the back of the seat/above the trunk covered a screw that was holding the speaker in and we didnt know how to remove it. What should we do ?