1. Boot into Clockworkmod recovery mode (From powered off state, hold vol-down, home, and power
button until the LG logo appears).
2. BACKUP ORIGINAL ROM! use vol-up/down, camera, & back keys to navigate in recovery.
3. Factory Reset, wipe cache & dalvik-cache, then format all partitions EXCEPT /sdcard.
4. Flash the custom ROM.zip from sdcard and gapps.zip too if going to a CyanogenMod ROM
5. Reboot and enjoy the new ROM, the first boot takes longer than usual, also some problems may disappear after rebooting.
This was a copy and paste from the stickie Whyzor has at the top of the forums.
DO NOT TRY TO FLASH THE ROM FROM THE APP INSTALLED ON YOUR PHONE it currently dose not work for the V once you have the recovery installed from Rom manager its best to delete it unless your going to use it to rename backups.