If you're using VCDS then when you go into the coding window, if you wait a bit it ought to show the popup that tells you what coding means what. It's also listed in the back of the Bently, Volume two. The AWM engine's chart is on page Z-27.
This is assuming the coding will work the same on the chipped ECU(If it shows seven digits for the current coding, make sure the first two digits remain 00):
Digits 1 and 2 of 5(or 3 and 4 of 7) are the emission standard:
07 = LEV(Low Emission Vehicle)
16 = ULEV(Ultra-Low Emission Vehicle)
Digit 3 of 5(or 5 of 7) is the drive type:
0 = FWD w/o ASR
2 = AWD w/o ASR
5 = FWD w/ ASR
7 = AWD w/ ASR
Digit 4 of 5(or 6 of 7) is the transmission type:
0 = 5-Speed Manual
1 = 6-Speed Manual
5 = 5-Speed Automatic 01V (Tiptronic)
And finally the last digit will always be 1, which basically means it's a B5 Passat.
For example, my '04 1.8t wagon with the 5-speed manual and FWD w/ ASR codes as 16501 or 0016501. All American cars should read 16 for the first two, if I remember correctly.
As far as the immobilizer stuff, I do not know how to do that, it's not something I'm looking at needing to do in the near future. There should be plenty of info on the forums for it though.