I have been using DD-WRT with a WRT54GS for a while now and have liked it, but I wanted to try something different with my new WRT350N,  I flashed it via the web interface on the stock Linksys firmware with snapshots/bcrm-2.4/openwrt-wrt350n_v1-squashfs.bin.  Looking back I realize this wasn't a good idea.  However, the firmware did go in fine, but the router started acting a little wonky, so I restarted it for the firmware to take effect.  It booted up fine, except for the fact that the interfaces weren't setup up right, and I can't connect to it anymore.  I spent the next two hours researching what I can do to get this thing back, but I had no luck with TFTP as there was no connection between my computer and the device.  I tried different kinds of combinations, but when I plugged the WAN port back in, I noticed on bootup that the router was accessible for ~4 seconds.  Using this little opening, I tried to TFTP the stock Linksys firmware back in, but it fails.  All the data is transfered, but it fails with error code 13.  I tried using DD-WRT mini for a 350N, and that is fully transfered, but the reflash never takes place.  The router just idles.  After a TFTP I can ping the router for several minutes, but after that connection just fades.  I haven't opened it up yet, but I am willing to do that.  I am also willing to buy a JTAG cable, or solder in a serial cable if needed.  Any help would be great, and thanks for reading.

With a little more research, I was able to do a successful TFTP transfer.  Directions for what worked for me:
https://dd-wrt.com/phpBB2/viewtopic.php?t=25637