I have a 2003 Nissan Xterra XE. The SE Model is the one with the aux port and the nice rockford fosgate sound system

. I'm fairly new to this so what would you guys suggest I do? Here's my plan so far:
-Stock speakers(I guess I'll have to replace these)
-OPUS 150w PSU - $140
-Old Computer(400mhz 96mb 8gb) - free
-280 Watt Alpine Amp - free
-Palm Vx(to control mp3s) - free
-mp3car 3.5mm to RCA cable adapter: $8(would i need 2 of these and a y-splitter for the sound card, or could i just use one of them? i'm clueless when it comes to this stuff. the amp is 4/3/2.)
Power inverter(for palm pda) - (about $30 ebay?)
Stereo cables to buy:
-Power(amp to battery) : $$$?
-Power(OPUS to battery?): $$$?
Budget: $220(will slowly increase more as time goes on and i pay more of my car note off, at which time it will greatly increase)
-OPUS($140)
-3.5mm to RCA Cables($8?)
-Power inverter for palm(??$30??)
Money Left: $42
Can it be done? Is it logicial? Will $42 in speakers sound like crap? Should I just wait until the speakers blow then upgrade them? Should I just buy $21/speaker for fronts and upgrade rears later?

I've been reading a lot and learned about the computer side but have been trouble finding things on car audio since I'm very unfamiliar with it.
My carputer is going to be a slow building project as i receive more money to put into it. I am debt free aside from my car note(about $2500 left

) and would like to keep it that way.
OS - TinyXP
Programs running at beginning: Winamp(instead of Windows Shell)
Time from boot until playing music: 55s
Future - Lilliput, GPS, FM Radio, Bluetooth phone control, Wi-fi card
(After I get my carpc set up I'll sell my Garmin iQue M5 PDA/w GPS for some cash to get more carpc components.)