From DD-WRT Wiki
Please see this thread for information on E1000 and dd-wrt compatibility http://www.dd-wrt.com/phpBB2/viewtopic.php?t=79673
 Install / Flash Linksys E1000 v1 only! (see above link for v2)
The following instructions are copied from Dark_Shadow's forum post / wiki see: http://www.dd-wrt.com/phpBB2/viewtopic.php?t=79673 (same as link above). I am adding them here after testing and validating they work as per his request in the forum. They worked flawlessly for me installing on a Cisco Linksys E1000 v1 [--Apus.one 05:08, 15 October 2011 (CEST)].
- Read the Peacock Announcement.
- Download dd-wrt.v24-15279_NEWD-2_K2.6_mini_e1000.bin. If you wish to experiment with a newer build, you should read the "build thread" for any build you are considering putting on your router, before flashing a newer build, (as discussed in the peacock announcement).
- Set a static IP on your computer to 192.168.1.7. Subnet mask should be 255.255.255.0
- Connect the lan cable from your computer to a LAN port of your router. Make sure your router is plugged in. Nothing should be connected to your computer or the router except the lan cable between them.
- Ensure you have a physical ethernet connection to your router, and disable your wireless adapter, antivirus/firewall protection, and any software that makes strong use of your network (BitTorrent, Streaming Audio/Video, etc).
- Perform a hard 30/30/30 reset.
- Navigate to http://192.168.1.1/ in your web browser of choice.
- At the Linksys Administration > Firmware Upgrade page, do not give the reboot command. You will use this page to upgrade your firmware.
- Browse to the firmware you downloaded and click Upload.
- Do not touch anything. The page will tell you that the upgrade was successful and the router is now rebooting. Your router may take upwards of a couple minutes to reboot. Watch the lights... once the wireless and power indicators are on steadily for several seconds, your router is fully rebooted and you can click "Continue" in your browser window.
- If the DD-WRT password change page displays, your upgrade has been successful, and you must now perform another hard 30/30/30. This time, when you navigate to http://192.168.1.1/, click "Reboot" and wait for the router to come online again so you can configure it.
If the DD-WRT password change page does not display, your page request times out, or you can't ping 192.168.1.1, make sure both wireless and power lights are on steadily first, then do a hard power cycle (unplug the power from the router--do not do a 30/30/30 reset). Wait a few seconds and plug the power back into the router. Wait until both wireless and power lights are on steadily, then navigate to http://192.168.1.1/ in your browser of choice again. If the DD-WRT password change page displays, your upgrade has been successful, and you must now perform another hard 30/30/30. This time, when you navigate to 192.168.1.1, click "Reboot" and wait for the router to come online again so you can configure it.
You can also flash the same firmware of TomatoUSB as described for WRT160N_v3.0
 Performing a 30/30/30 Reset on a Linksys E1000 v1.0
- Perform a normal 30/30/30 reset.
- Login to http://192.168.1.1/ and you will see the Linksys - Management Mode page.
- Click "Reboot."
- In a moment, you will see "Command reboot completed." The router will now start the reboot process. When the lights return to their normal state, you can click "Continue" to be taken to the router's main page.
 Serial Recovery
I had an awfully difficult time doing serial recovery on this router. It was my first time so you can imagine that I had no idea what I was doing. There are some slight deviations from the standard serial recovery procedure that is in the Wiki so I decided it would be a good idea to add the information here. First of all, the pinout is the same as the E2000 (at least for the E1000 v2).
You should familiarize yourself with the Serial Recovery article before trying this, I'm not going to explain everything again here.
Looking from the back of the router you should see the 2x6 JTAG port and above that 5 holes. These 5 holes are the serial port. Again, looking from the back of the router: VCC - RX - TX - ? - Gnd
Once at the prompt you need to assign an IP/Subnet mask to eth0. I'm not sure if eth0 is the routers interface to the switch or one specific port but I had a CAT5 cable hooked up to port 1 on the router and it worked.
If you type "ifconfig eth0" you will see that there is no address assigned to the interface. The following command will assign an address/mask.
CFE> ifconfig eth0 addr=192.168.1.1 mask=255.255.255.0
Now you can flash using a TFTP client from your computer, which is plugged in to port 1 on the router, just like the Serial Recovery page says.
Barryware, using a mixture of perseverance and brilliance, has found a way to fix the fact that Linksys, in for completely baffling reasons, did not connect the jtag port to the processor. This isn't for the faint of solder, but there IS now a way to jtag the 160nV3 and the E1000_V1! See this: http://www.dd-wrt.com/phpBB2/viewtopic.php?t=146077
flash -ctheader : flash1.trx