After copying the zip file to the sd card what exactly i need to do to flash the rom?
Hmm...don't want to be a jerk, but you might want to do some more reading about Clockwork before you go flashing.
The ROM .zip file needs to be on the root of the internal SD card, that is, /sdcard
From there you would reboot into Clockwork (this can be done from ROM Manager) and once there (should be a green menu...if you see a blue menu you are in stock recovery) you can manually choose to pick the .zip file you want to install. I don't recall the exact choices, but it should be obvious enough.
You navigate with the UP & DOWN volume buttons and select with the POWER button. Be sure to pick the correct file. You didn't rename the file, did you? There is no reason to. Some people mistakenly rename it to "update.zip"
Once the ROM is flashed (not long...5 minutes or less) you will be back at a menu. Choose "Go back" and from the subsequent menu choose to reboot the system.
Wait 10 or 15 minutes after the phone boots to start playing around with it. Look around for a few minutes then reboot again. Things should be in order by then.
Have you read about Odin? I would advise you to do so and become familiar with it. If a flash goes bad, and it does happen, Odin might be the only thing that gets you back on your feet.