7. Rename the rom file you downloaded from whatever.nbh (usually it is ruu_signed.nbh) to Kovsimg.nbh (you can rename it on your pc or on your phone once you have transferred it over)

8. Start up the phone normally, if you have not already done so...then connect it to your pc...(at this point you can connect it without activesync, just as a memory card reader so that you can copy over your rom faster)
Copy your rom into the root of the memory card.
(You can also use any external memory card reader/writer connected to the pc and copy over the file)
Remeber to make sure all files have been deleted off your memory card.

9. Insert the memory card into the phone (You never know somebody might forget to do it :-S )

10. Turn off the phone completely, not standby mode (USB cable must not be attached)

11. Remove and reinsert the battery (This step can be skipped if you made sure you turned off the phone in step 10, this is just in case somebody put the phone in standby instead)

12. Hold down the volume down button and press the power button while still holding both of these buttons until the tri-color screen pops up.

13. Follow the onscreen instructions (It should install the rom +-5mins)

14. When you see the screen say "Succesfully updated", you can then go ahead and remove the battery and reinsert it.