Tak už jsem to trochu pochopil a podle těchto návodů bych to měl zvládnout, akorát bin soubor musím mít pro v1:
http://www.copyrunstart.net/installing-dd-wrt-firm ware-on-asus-wl-500gp-v2/
http://www.dd-wrt.com/wiki/index.php/Asus_WL-500g_ Premium_V2

Flashing
The easiest, most reliable method to flash to 3rd party firmware is to use ASUS Firmware Restoration tool that comes on the CD bundled with the product. There is no firmware size limit requiring you to flash dd-wrt mini first; you can go ahead and flash dd-wrt mega right from the start.

When flashing from 3rd party firmware to other 3rd party firmware, just use the firmware upgrade utility in the web GUI. This applies to 3rd party firmwares that include a web GUI, as not all of them do so.

The ASUS Firmware Restoration Utility comes with the CD-ROM included with the device and by default installs to
WinXP / Vista 32-bit C:\Program Files\ASUS\WL-500gP V2 Wireless Router Utilities\Rescue.exe
Vista 64-bit C:\Program Files (x86)\ASUS\WL-500gP V2 Wireless Router Utilities\Rescue.exe
[edit] Flash using recovery method

To flash using the "recovery" method, do the following...
1) Unplug the router
2) Press and hold the black restore button and plug in power.
3) Keep holding the restore switch until the power light starts to blink on and off.
3a) The router is now in recovery mode
4) Change the ip settings on your computer to:
4a) IP: 192.168.1.xxx(use anything above 1, I like 100)
4b) Subnet: 255.255.255.0
4c) Gateway: 192.168.1.1
5) Run the recovery program and point it to your .bin file of choice
6) Hit the "upload" button and wait about 2 minutes.
7) Change your IP settings back to DHCP and let it get an address
8) Open a web browser and go to http://192.168.1.1 and have fun!