i have a asus rt-n16 with dd-wrt on it and now want to try out tomato but haven't found a tut on how to install it.
You should be able to flash it right from the DD-WRT upgrade screen. In fact, it is common to flash the N16 with DD-WRT mini before flashing with Tomato, as an interim step. That is what I had to do because I never could get the Asus Firmware Restoration Utility method to work.
After flashing, do a complete reset with erase all NVRAM and wait a full 5 mins.