The AVM ARC upgrade is only available for the AVM-30HD (i.e., the one that's already been upgraded to add a video board), the AVM-40, and the AVM-50. It is not available for the original AVM-30 (unless you send the unit to the factory to get the video board added) or AVM-20, nor, we've been told, for the AVM-20HD.
The upgrade involves replacing the single DSP hardware in the AVM with a dual DSP. This change is dealer installable, i.e., you don't have to send the unit to the factory.
You get the dual DSP change-out, plus the ARC application software itself, a specially calibrated microphone, a longish mic to USB cable, and an OK but not great mic stand for $800 (plus perhaps a bit of labor charge at the dealer for the hardware install, which only takes about 5-10 minutes).
If you don't already have one of these AVM units, you can also buy a NEW AVM-40 or AVM-50 factory bundled with the dual DSP and ARC for $500 over the previous pricing (all pricing is Anthem's MSRP).
It is shipping now. Order it through your Anthem dealer. A number of us here have also purchased a $30 boom-style mic stand (from some other source) to use instead of Anthem's included stand.
Setting up ARC is ridiculously easy and well worth the effort. Some people experiment with re-doing the Measurements or playing with ARC's default "Targets" for Calculation, and of course that takes more time if you want to do that, but not all that much more time.
You need to take a bit of care in a few preliminary steps in the Anthem, and in your choice of microphone locations during the ARC Measurements, and you need to make sure ARC is turned on in the AVM after you Upload the ARC results to it, and that you Save the resulting Setup menu settings after the Upload.
You will also need to upgrade your AVM to the V1.33 firmware (or newer) prior to running ARC Measurements. At the moment, the latest ARC software is V1.2.5 and you should download and install that one if you get shipped an older version from Anthem.
You will need a computer running Windows XP or Vista with one USB port for the microphone cable and either a real serial port or a separate USB to serial adapter plugged into a second USB port for communicating with the AVM during the setup. Most folks are using a laptop for this. A wireless mouse makes it easier to get out of the way when doing the ARC Measurements. The Keyspan USA-19HS USB to Serial adapter works well (with the latest driver from the Keyspan site).
The Measurement and setup process can easily be done in an hour -- probably more like half an hour if you are organized. You will need a time when there are no significant external noises in your listening room that would interfere with the ARC Measurement process.
The ARC V1.2.5 install kit is available for download now from the AVM downloads page on the Anthem site. In that ARC install folder you will also find an updated Operating Manual for the AVM-40 and AVM-50 (combined now in one Manual). The new Section 3.15 in that Manual describes the ARC setup process.
Lots of notes on setting up ARC and what it does for you are in this thread in the pages dating back to April when the ARC upgrade first shipped for the D2.
One very important thing to be aware of is that the two ARC licensing and calibration files that come on its install CD will set ARC to work only with the specific serial number of your AVM (and the mic shipped with your copy of ARC). That means it is crucial that your dealer send in the correct serial number for your AVM when he places the order, and that you get delivered the ARC kit intended for your AVM if he receives more than one of them from Anthem at the same time. You get the serial number for your AVM by pressing Select repeatedly on the remote. The last set of info that gets displayed before it starts over again includes your unit's serial number.