From DD-WRT Wiki
 Hardware Information
|CPU Speed||400 MHz|
|Flash ROM||8 MB|
|Radio||1x 2.4 GHz|
|WLAN Max Speed||300 mbps|
|Antenna Location||2x external (RPSMA)|
|Switch||4x 10/100 + 1 WAN|
|USB||1x USB 2.0|
 Flashing instructions
You will first need to download this file for the flashing.
1) Go into the linksys stock firmware and choose to reset to defaults.
2) Once that is finished, set a static ip on your machine to 192.168.1.6 with subnet 255.255.255.0 and gateway 192.168.1.1
3) Log back into the linksys firmware and find where to update the firmware.
4) Select the file linked above and then begin the flash procedure, this usually takes 6-7 minutes for it to finish properly, so be patient!
5) Once it is finished, close your browser, then reopen and browse to http://192.168.1.1 it should want you to set a user/password, do so.
6) When you are in dd-wrt's webgui, go to Administration > Factory Defaults
7) Select to "Restore Factory Defaults" This will effectively hard reset the router and ensure integrity of the flash.
8) Log back into the webgui @ http://192.168.1.1 and set a user/pass and enjoy dd-wrt!
- Should you want to use DHCP you then may want to unset the static ip from your machine.
 Reverting back to stock
Should you want to revert back to stock firmware then you should be able to download the stock firmware from Linksys's site and flash back using the webgui.
 Useful Web Links
Here is the link for the forum support topic regarding E2100L.