Booting back to stock from other patition
When you install DD-WRT over stock, it installs on a different partition. You can use the following command by entering it in DDWRT commands on the administration tab, Telnet or SSH to determine what partition DD-WRT is running on.
Code:
ubootenv get boot_part

The last number it returns is the partition (it will return 1 or 2). In my case, DD-WRT is on partition 1, so to return to Stock, enter (If yours returns 2, put 1):
Code:
ubootenv set boot_part 2

and then reboot. You can use the command
Code:
reboot

To reset and boot to stock if you brick DD-WRT installation
1. Assuming the router is on, turn it off.
2. Turn it back on... the power light will illuminate and then go out briefly as it prepares to boot. As soon as it goes out, turn it off again. Repeat this step three times, leaving the router on after the third time you turn it off.
3. Let it boot. It should return to stock after you let it boot.