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Edit: this applies to 2003+ B6 models. The 2002 has a different CCM, and the lock/unlock/panic buttons will not work on the key remote. Credit goes to audballz for pointing that out.

There are already a couple of threads out there on how to make a B7 key work with a B6, but mine is different because I didn't swap or sacrifice my B6 key. I purchased two B7 keys and installed new blades and immobilizer chips. Since my car only came with one key, and I drive it daily, I recently felt the need to purchase extra keys just in case. This process worked for me, and because of my schedule, took a month or two to complete - it may or not may work for you, so be prepared before you start, and if you screw up it's not my fault.

I have laid out the steps here, and it seems fairly easy, but one must be willing to be persistent and put a little work and have the tools to do the job and get it done. Now, the standard disclaimer - this thread contains the steps I took to make B7 keys work with my B6. Your experience may or may not be similar, and I will not be held responsible or accountable for any mistakes or issues you have in following my experience. This is strictly a guideline, your experience may very.
Cliff notes:
First, I found used/new keys off of eBay, then ordered a couple of key blanks for the B7 keys from a seller on eBay. After I got them in the mail, I assembled them and then could have the keys cut to match, and I had to find a local locksmith who was able to cut the Sidewinder key. I then needed "virgin" B6 immobilizer chips so the dealer could program them to my car (the B7 or any non-virgin IMMO chip would not be able to be programmed) so I had to order those. Once the virgin B6 IMMO chips were installed in the B7 key, I took my car to the dealer to have them programmed. The result is 2 B7 keys and 1 original B6 key.

Hardware list:
Immo Chip(s) - ID48 MAGAMOS 48 https://www.keymam.com/product_view.asp?pid=50
B7 Key blank(s) - eBay seller "artiway" http://ebay.com
B7 Keys - Both were bought on eBay from various sellers. Both these part numbers below work for me - there may be others:
8E0 837 220 R - various seller with a used key (key was cut already)
8E0 837 220 L - seller was "midwestkeyless" (came with a new key blank installed)
4F0 837 220 N will not work with the B6.

Vag-Com - get it from Ross-tech.com or find a buddy http://ross-tech.com

Steps to complete the process:
1. Buy B6 immo chips from Keymam ~$5.00 each
https://www.keymam.com/product_view.asp?pid=50
2. Buy B7 key(s) - eBay is a great resource ~$40 each
3. Buy B7 key blank(s) - eBay is a great source ~$15 each
4. Put new key blank(s) in key(s), and install new (virgin) immo chip(s)
It helps to follow this thread http://www.audizine.com/forum/showthread.php?t=199643
This will tell you the basic process of swapping immobilizer chips and key blades 

Here's some pics on how to pull the IMMO chip:

See the gold lettering - this is from an Audi A6

This is a pic with the IMMO and holder out of the key. Carefully pry around the grey plastic part (it will be in the red circle area) and remove it from the key.The IMMO chip is glued/set in the grey plastic part - carefully pull it out and put your virgin B6 IMMO chip in it's place.

This is a pic of the key part # - I can verify that both my B7 Keys work with my B6.


5. Take keys to a locksmith to have key(s) cut ~$30 per blade
Make sure the keys work in both the door lock and ignition or take them back for a recut/adjustment
6. Keymatch remotes using Vag-Com:
Again, go to this thread http://www.audizine.com/forum/showthread.php?t=199643 or follow the below:
Start Vag-Com
Choose [46 - Comfort System]
[Adaptation - 10]
Go to channel 021.
[Read]
* Choose the memory position you want the new key be matched on by entering it's number (e.g. "3" for memory positon 3).
[Test]
* Now press any button on the remote you want to match.
* The meas. block field above will change from Not Recogn. to Recognized.
[Save]
7. Take keys to dealership to be immo programmed ~$80
Make sure to take all of them - they all need to be programmed at the same time, and plan to pay for 1 hour of labor.
So, for about the cost of one single new programmed key from the dealer (~$250) I now have two new B7 keys, and one original B6 key. All remote functions work and all keys start the car.