Please note the following information is based on my personal experience and knowledge only. You have been notified on the risk involved, I'll not be held responsible for any causes to your device either before, during or after OpenWrt flashing, you are doing this at your own risk.
Please read through the following, learn and understand better before start flashing to OpenWRT
Official website : http://www.openwrt.org/
Router compatibility & supported devices : http://wiki.openwrt.org/toh/start
Flashing Guide : http://wiki.openwrt.org/toh/start (select the device link)
FailSafe : http://wiki.openwrt.org/doc/howto/generic.failsafe (to recover/revert)
Firmware (stable released version) : http://downloads.openwrt.org/backfire/
Useful tools (need to learn & know how to use) :
If you like OpenWrt, please donate some money to them to show your support and appreciation. You may also consider to donate routers for their R&D purpose.
Those OpenWrt developers really spend a lot of efforts in making this wonderful firmware to benefit us, a small donation and give-back may not means anything to us, but it will certainly recognise their great efforts to continue making better firmware for our routers!!
By flashing the router with 3rd party firmware like OpenWrt, individual owner must aware that it will void the manufacturer warranty, risk for unable to flash back to original manufacturer firmware, possible to the extend of bricking the device!