To check if you do in fact have a nandroid backup, you should look in your /sdcard partition and see if /clockworkmod/backup/(date of backup)/ exists. You might want to copy the contents off this folder as a belt and suspenders kind of precaution. Speaking of backup, if you've copied all the data off the phone that you wish to protect, then we are ready to flash.
This should take 20-30 minutes depending on how quickly you execute the steps.
First thing you want to do is make sure the phone is fully charged since this is all done with the phone unplugged. Nothing will brick a phone faster than dying in the middle of a flash.
Now, ready? Take a deep breath ... take another ... don't hyperventilate.
Copy the rom file (keep it zipped, do not expand the files) to the root of your
internal SD card partition. Yours will be something like "Doc's_Master_ICS_Rom_V3.1_by_VibranTurk-Cappy.zip" and should be around 133MB.
Boot into Clockworkmod Recovery. Shut down the phone. Pull the battery for a second or two, remove the exrternal sd card if there is one, and the sim. Put the battery back and close 'er up. Press and hold the vol up and the vol down buttons then press and hold power. The second time the screen flashes the splash screen, release the power button but keep holding the volume buttons. Once you get the recovery screen, release the vol. buttons.
Use the vol. up and down keys to select the options and use the power button to confirm your selection.
Select wipe data/factory reset. This will remove your personal data and put the phone in a clean state. It is important to do this when flashing any rom. When that option is highlighted, press power to select. You'll have to scoll again to the confirmation and press power again. This operation is pretty quick. When done, press the back button as many times as necessary to get to the main CWM screen.
Clear the caches. Some say this is optional for roms, but because this rom includes a new kernel too, I always do this. Same method ... highlight wipe cache partition. Press power to select. Scroll to confirmation and press power again to wipe. Then back to the main CWM screen. You should also wipe the Dalvik cache at this point. If it's not in the main cache wipe options, it will be under advanced.
Install ZIP from SD card. Highlight and press power to select. Scroll to the rom zip file which will be pretty far down if you have a lot of folders on your sd card. when you have that highlighted, press power to select and again confirm as before. Now you are installing the rom. This takes a while as it flashes a new modem, new kernel and then installs the rom. Let it run and be patient. A couple of times it may appear to stall for as long as several minutes, but that's normal, just let it go and don't panic and restart the phone until it tells you it's done. When it is done, go back to the main CWM screen and reboot. The first time it boots it sits on the splash screen a while while it builds the files, so again, be patient.
Congrats, you are now on ICS.
