I would reccomend looking at other amplifiers than Alpine, as there is a lot of quality out there... namely the US brands: Boston, Phoenix Gold, just to name a couple i have dealt with.
PS2 will fit under the passanger seat, all you need to power up is a transformer 12VDC-240AC (available from most Auto shops). Alternatively you could modify the PS2 itself and run 12VDC directly to the PCB in the PS2 if you know what you are doing.
Personally, i would highly recommend XBOX due to its inbuilt HDD, and capabilitys as a Media Centre, once it has a modchip installed. this will help greatly when driving on bumpy roads! You will also save money on having to buy and extra DVD player for the TV screen, unless your deck is DVD capable.
Dont forget about cabling and sound deadening...
I just recenlty spent $1500 on cabling, sound deadening and optima battery. No point getting compettition components without installing it properly IMHO.
Also i wouldnt worry so much on getting top end speakers for the parcel shelf, as their main purpose is primarily for refill, and SQ isnt really a main factor when you have a quality front stage!
If you are interested in some prices on a high end setup, drop me a PM, or add me to msn and i should be able to help you out!
PM me if you want my msn details, and ill help you out as much as i can.