Building a PC fast, is easy for me. But I'm afraid I'd get stalled out with the in-dash unit. I've got an Alpine amp and Kicker speakers (behind the seat), from my other S10.
Would Best Buy have any problem installing them with the CD/MP3, or would they balk at that?
They'll charge you more for it, and do a terrible job. If you really are dead set on having it installed, go to a real car stereo shop and have them do it. They'll probably charge you more for the wiring harness/install kit too.
I did it on my 95 Blazer, it was pretty easy, did the whole thing in under a day. The reason it took as long as it did was two-fold. First, I hooked up my CD Changer to the wrong input on my radio (the non-volume modulated one - so the volume was at max no matter what the radio was set at) and second, the antenna adapter gave me all kinds of trouble. The one I bought had a long plug on it connected to a flexable cable for the OEM antenna hookup. The problem is, because the connector was so long, it kept hitting the back of the "well" for the radio. I had to custom make an antenna adapter out of the one I bought - it's probably not as good as the unmodified one, but I have XM and a CD changer, so I very rarely listen to the radio.
The damn CD Changer thing really baffled me - I don't remember how I thought to check the inputs
Like I said, spend the extra cash and take it to a professional stereo place, I've got to think it'd be worth it. Bestbuy installed a stereo in my sisters car, in the process they screwed up the alarm and half her dash lights didn't work. She took it back, they "fixed" it, but they never assmbled the dash correctly so it kind of looks screwy.