You should use these 2 threads:
http://forum.ppcgeeks.com/showthread.php?t=42503 (for unlocking)
http://forum.ppcgeeks.com/showthread.php?t=43266 (for flashing)
But to summarize, here are the steps for unlocking and installing a ROM
First thing you'll want to do is unlock your phone.
I, for example, am with Sprint, so I use the file:
"Raphael_CDMA_HSPL_037"
How to Unlock:
1. Make sure you have your phone connected via ActiveSync/Windows Mobile Device Center
2. Double click the exe file (in my case, "Raphael_CDMA_HSPL_037") to extract it
3. Run it, and follow the prompts on the screen (keep clicking next)
4. Your phone should now enter a tri-color mode (Red, Green, Blue)
5. New SPL flashes onto the phone, and the phone automatically reboots
It should now be unlocked
How to Install a ROM
1. Make sure you have your phone connected via ActiveSync/Windows Mobile Device Center
2. Download your ROM of choice (I use Mighty ROM)
http://forum.ppcgeeks.com/showthread.php?t=52695
3. It will be a rar file, so extract it to a folder of your choice
4. Upon extracting, you will find an exe file called "Custom_RUU"
5. Run it, and follow the prompts on the screen (keep clicking next)
6. About 3-4 minutes later or so, the phone should now be flashed to the new ROM
It is suggested to Hard Reset your device before and after flashing (to remove any potential junk that may still be floating around), and the way to do that is:
How to Hard Reset (optional):
1) Turn off device (by either holding down the power button or by taking off the back cover and lift the battery out slightly then push it back in so the battery is reinstalled but power still remains off)
2) press and hold the Volume down button while at the same time pressing the center "Enter" button. Keep them pressed
3) While volume down and enter buttons are pressed, press and HOLD the power button until you see a screen that says:
"This operation will delete all your personal data..." <rest of verbiage snipped.
4) Follow those on-screen instructions which will tell you to push the volume up button to continue performing reset.