Hi, Everyone,
 
  I've read through the WNDR3700v2 info on the HW wiki at http://wiki.openwrt.org/toh/netgear/wndr3700 but I'm still a bit confused on exactly which file to use for the initial flash.

  Given the fact my new WNDR3700 is, in fact, v2 of the hardware, I understand that I need to use the most recent RC of "Backfire," v10.03.1-rc5, for it to work.  I also understand the devs recommend the squashfs images...  that being the case, then, there are three possible files:

openwrt-ar71xx-wndr3700v2-squashfs-factory.img
openwrt-ar71xx-wndr3700v2-squashfs-factory-NA.img
openwrt-ar71xx-wndr3700v2-squashfs-sysupgrade.bin

  If I'm trying to flash the router which is currently running the Netgear image, which do I use?  I am located in North America, so is that what the "NA" tag means on the second file?
  Being new to OpenWrt, are the "sysupgrade" files used for upgrading a router already running an older version of OpenWrt?

  I apologize in advance if this is listed in detail elsewhere; I searched the OpenWrt forums and Wiki about the WNDR3700v2 and didn't seem to be able to find a step-by-step guide with specific filenames...  just wanted to be sure I had the right info before I got started...

  Thanks very much in advance for any assistance!

It occurred to me the router is new and returnable so I might as well try it and see what happens...

I used the 10.03.1-rc5 file "openwrt-ar71xx-wndr3700v2-squashfs-factory-NA.img" and, thankfully, it flashed fine.  Hope that was the right one! 

Initial impressions with OpenWrt compared to dd-wrt is that this looks very nice!  I'll try messing around with the wireless radios this weekend.

You got the correct file, (even the NA = North American version for avoiding Netgear firmware warnings during the initial flash).
If future, use the sysupgrade for upgrades from existing Openwrt systems. (And then again factory, if you need to use the failsafe mode to recover from a bad flash.)

Ps. There are also ready-compiled tailored versions available for 3700 (from the Community releases section of the forum) with all the buttons working etc. If you are interested, check Arokh's and my threads in that section.