It's up to the app's developer to set the constraints in the market. It's up to you to read about what you are installing on your phone. You have an Optimus V, not a Galaxy S, so don't install software meant for another phone.
Now you are going to have to use ADB to get things going again. Start by downloading and installing the Java JDK. Next, download and install the Android SDK.
Next, download the Xionia recovery, and the ROM of your choice (and any other files the ROM needs like gapps for aospCMod). Once downloaded, move them into your Android-SDK's platform-tools folder.
Edit: It's sometimes hard to tell where the spaces are in these commands, so I put a red underline "_" in place of all spaces below.
Next, connect your phone to your PC via USB and turn it on. Once it has started up, open a command prompt on your PC and type the following:
cd_c:/PATH_TO_ANDROID_SDK_HERE/platform-tools
adb_shell
If you get a successful adb server running, you should then see eithr a $ sign prompt, or a # sign prompt. If you see a $ sign, you are not rooted, stop here and post that you are not rooted. If you see a # sign, you are rooted, continue.
Now type
exit
Now type the following:
adb_remount
adb_push_c:/PATH_TO_ANDROID_SDK_HERE/platform-tools/NAME_OF_ROM_ZIP_FILE_/sdcard/NAME_OF_ROM_ZIP_FILE
adb_push_c:/PATH_TO_ANDROID_SDK_HERE/platform-tools/NAME_OF_XIONIA_RECOVERY_FILE_/sdcard/NAME_OF_XIONIA_RECOVERY_FILE
adb_shell_flash_image_recovery_/sdcard/NAME_OF_XIONIA_RECOVERY_FILE
adb_reboot_recovery
Your phone should now boot into the Xionia recovery, title at the top and bottom, with menus in blue. Use your volume up/down to navigate the menus, the menu_key to select an item, and the back_key to go back to the previous menu.
1) Select wipe cache
2) Select advanced, then select wipe dalvik cache
3) Select mounts, then format data, cache, system, and boot
4) Back in the main menu, select install zip from sdcard
5) Select install zip from sdcard (DO NOT CHOOSE TO UPDATE ANYTHING!!!)
6) Select the ROM zip file (this will take 2-5 minutes to install, be patient)
7) If your ROM had other files such as gapps, install them now
8) Back in the main menu, select reboot system now
Your phone should now reboot, it will take a long time, it has to rebuild all your system files, be patient. It should take 3-10 minutes, if it takes more than 20 there is something wrong.