I have the latest stable release, Backfire 10.03, running successfully on the WNDR3700 in case anyone is looking to do this.

Lots of helpful information in this thread as well as other threads there (use search for samba3 for instance or CUPS or bjnp backend for cups):

https://forum.openwrt.org/viewtopic.php?id=22311

You can check out this wiki page:

http://wiki.openwrt.org/inbox/netgear/wndr3700

On the wiki page when it tells you what to check out for svn you can either use trunk as it says, which will now give you the latest backfire code, or you can use the latest stable branch by doing the following:

svn co svn://svn.openwrt.org/openwrt/branches/backfire

cd backfire

./scripts/feeds update -a

./scripts/feeds install -a

make menuconfig

Also, in addition to the necessary packages for prepping the build environment mentioned in the wiki you also need libncurses5 (and/or libncurses5-dev, I forget which as I have both installed) under Ubuntu 9.10. Hope this is helpful; it is much better firmware than the factory firmware!