[EVO 4G Q&A, Help & Troubleshooting] drmacinyasha:
1) Flash the stock rooted 3.70.651.1 ROM from my link above (here it is again), via ClockworkMod Recovery.

I'm going to assume you have an older phone with the older partition structure. For more information, and to tell what structure you have, check out this thread once you complete Step 1, before you do Step 2. I'm also going to assume you have the Android SDK installed and set up. If you do, just open your Command Prompt, cd to your SDK\platform-tools folder, and run the command "adb shell cat /proc/mtd" (without the quotes). If you see an erase size of 20000, then continue. If you see 40000, STOP and let us know.

DO NOT CONTINUE IF YOU HAVE THE NEW PARTITION ERASE SIZE OF 40000!

2) Once you boot up into the ROM, download ROM Manager from the Market, if it's not already included in the ROM. You will of course have to add your Google account in order to access the Market.

3) Open ROM Manager, scroll to the bottom, and tap "Flash Alternate Recovery"

4a) Once it has finished flashing, download CyanogenMod 6.1.2 using your browser at the above link (here's the link again). You'll want the file update-cm-6.1.2-Supersonic-signed.zip.

4b) Also download the attached FORMAT_ALL.zip. This will help ensure you don't have any files from Sense accidentally carry over into CM.

4c) Finally, download the latest HDPI Google Apps package from here (the latest one has a link at the top of the page, and is the gapps-hdpi-20101114-signed.zip file).

5a) If you downloaded via your phone, use a file manager of your choice (I like Root Explorer, but there's free ones like OI File Manager in the Market) to move the three ZIPs from /sdcard/download/ to /sdcard/ (aka, the root of your SD card).

5b) If you downloaded via your computer, attach your phone to your computer via USB, turn on Disk mode, and copy the three ZIP files to the root of your SD card.

6) Power off your phone, then hold down Volume Down and Power to turn it back on. If you're taken to a white screen with skating Androids on the bottom (aka, hboot), then press Volume Down until RECOVERY is highlighted, then press the power button.

7) You should now be at a black screen with yellow text. This is Amon_RA recovery. Press Volume Down until you highlight Backup/Restore, and press Power. Press Volume Down and highly Nand Backup, and press Power again. Press Power one more time to confirm the start of the backup. It'll then take a few minutes to perform the backup (depending on how fast your SD card is).

8) Once it's done, you'll be back at the Backup/Restore menu. Make sure Return is highlighted, then press Power. Press Volume Down until Flash zip from sdcard is highlighted, then press Power to select it. Use Volume Down to highlight FORMAT_ALL.zip and press Power twice to select it, then confirm the flash.

9) Once that's done, scroll back to Flash zip from sdcard, then select update-cm-6.1.2-Supersonic-signed.zip. Press Power twice to select then confirm it.

10) Finally, go back to the Flash zip from sdcard menu one last time, highlight gapps-hdpi-20101114-signed.zip, and press power twice to select and confirm.

11) Finally, select Reboot phone now, and wait. The first boot will be a few minutes (it has to rebuild its caches), but after it's loaded, the Tutorial "Welcome to your PC36100" screen will show up. Congratulations, you have CyanogenMod!