the numbers are the chassis number used in developing the car...like back in the day, you had the e20 and the e30, e34, the e36, e39, e46 and so on...these refer to all the possible chassis that BMW has designed over the years. Between the e34 and e36, there was an e35 which I have never heard of, but that is because it most like didn't get approval for production. Then came the e39 which was an approved design for a car after three previous attempts.
In a short, yes its engineering code for the different chassis they have come up with. Hope this made sense... I think the new 3 series coming out in 2005-2006 is designated the e90. that means they went through about 30 different designs after the current 7 series before coming up with an approved new 3 series...
5 Speed Manual
Alpine CDA-7895 Head Unit
12" Alpine Type-R, sealed box
Pioneer 400w amp for $20 at a yard sale (to replace my fried MRV-1507)
Infinity Kappa 4" 2-way speakers(rear)
Infinity Kappa 5.25" component speakers(front)
Debaffled airbox, K&N filter
Tracked Mud on carpets
Shampooed and cleaned carpets