The hardest part of coding is downloading all the right software. These are HUGE files, so you need something like usenet or other deal. Basic zip programs like WinZip will not cut it. Many are RAR files for those who know what those are. I actually don't have a clue what they stand for.
Then make sure you buy the proper cable. When you browse through the coding section in the 3-series forum, you can read post ater post about people asking, is this the right cable? What about this one, it's $20 cheaper. Jeebus, just buy the right cable and don't screw around. If you have everything right, but the wrong cable, you will kill your cat or dog.
And, if using Windows Virtual PC so you can run 32-bit crap, you need to activate the OBDII cable using the menu option at the top of the screen. I forgot about that several times and it took weeks to get my hair back.
Start here.
http://www.e90post.com/forums/showthread.php?t=451145
It even has an excel page that lists all the coding options and codes to change. It's only like 4,700 posts,
but the beginning has a DIY. However, the software listed in the DIY is very old. You'l need to search around alittle for the most updated software. I bet there is a thread about recent software. The programs include NCSExpert, Ediabas, and INPA. I'm am far from computer literate and it took me bout 3 weeks to get it all figured out. I actually had to dump everything and start downloading all over again.
Here's a few threads where I worked through issues out loud. Might help you out if you try it.
http://www.e90post.com/forums/showthread.php?t=664603
http://www.e90post.com/forums/showthread.php?t=634863
http://www.e90post.com/forums/showthread.php?t=638152
I haven't bothered with upgrading my software for a few months, but this might be really helpful.
http://www.e90post.com/forums/showthread.php?t=629394