The first thing you want to do is order an M-class adapter from Becker. This will fit on car's harness and you'll solder it to the Alpine harness (supplied).
How much is the 9813? If you are buying it from Circuit City it is $399. The 9815 (much better) can be gotten cheaper elsewhere. I purchased it from
www.indoaudio.com for about $375. I also ordered a Kenwood Woox from him and should be getting it shortly.
Once you get the m-class harness, you can solder it to the alpine harness. You'll need to run a red wire from the battery to the alpine harness as well... use a red wire. If you want to use the factory amp, you'll need to run a wire (blue?) from the amps to the alpine harness. I think I can give you more specific details later.
Go ahead and get the M-Class harness from Becker... you'll need it regardless of who is doing it so that less cutting is required.