No need to do that actually. If you don't want to mess around with the cables etc, just assign yourself (your PC) a static IP address in the same range as your DNS323. You should then be able to access the admin page to change the configuration. Then reset your PC back to DHCP or assign a static address in the same range as your modem/router.
The other option is of course to change the default in your router to assign addresses in the old range.
Also, a crossover cable is never required these days. Most devices, including the DNS323, have autoMDX which will automatically do the crossover functionality.