I'm writing up the process that I used. There may be better ways to do it, but this should work for you. Most of what I've learned on how to do this has been gained from Modaco's ZTE Blade forum or xdadevelopers, I've just tried to cobble something together in 1 place for the P500.
I forgot to document wiping cache, etc. I'm adding it in now.
Before proceeding, make sure you've got plenty of charge in the phone. You don't want it to power off while flashing.
Installing USB drivers on PC
If you've already had your phone connected to your PC, you should be able to skip this bit. If LGMDP doesn't detect the phone later on, then you probably need to install the driver.
Download LG Mobile Support Tool from here.
You should get B2CAppSetup.exe. Run it & on the main windows, click Install USB Driver, then double-click on LGP500. Follow the instructions to install the driver.
After the USB driver had finished, it popped up an archive with an exe inside, presumably for using the phone as a modem via USB. I didn't bother installing at this time, I've no need of it. My LG software then gave me a bit of grief, so I closed it & rebooted. After reboot, I closed the LG software update app in my systray. I'll be remobing that, I don't need to know about software updates.
Have your phone powered up (I didn't have a SIM in) and connect it to USB. Windows should detect it & install the drivers.
Installing Clockworkmod recovery
Follow hecatae's instructions to install Clockwork recovery. Don't worry about Step 1, it isn't there, you're starting at Step 2. After Step 3, the Q&A part is to root the rom but there's no need if you're going to flash a new rom as you'll be overwriting the rooted one.
Mine took just over 2 mins and is a scary process if you aren't used to this, with warnings & the USB disconnecting & reconnecting. As stated, just leave it alone until it says Download Completed!
Backup up your old rom and installing the new one
Once done, the phone will be off. Disconnect the USB, then hold down <Home> and <Volume Down> while pressing <Power> for a second. The phone should start up. Let go of the <Power> button, keeping <Home> and <Volume Down> held for another second and it should boot into Clockwork recovery.
In Clockwork, the <Volume> buttons let you move up & down and <Menu> selects an option. <Back> goes back.
If you want to backup your existing system, go to backup and restore, then Backup. That will take a little while to backup your whole phone to the SD card. Wait until it's done, then you'll need to get the data from the SD card. Either switch off, remove the SD and connect to your PC using an adapter or select reboot system now to start the phone normally so you can use it to access the SD card. If using your own card reader, ignore the next step.
When the phone has booted, connect the USB cable and press Turn on USB storage on the phone when the option appears.
Copy the clockworkmod directory from the SD card to your PC. Keep it safe, this is your backup. If you lose this, you will still be able to return to a stock rom by downloading one from LG, but any changes you'd made will be lost.
Keep your SD card accessible, you're going to be putting new files on it soon.
Install new rom
Download devoid from here.
Read the thread, understand what you're getting and post any rom specific questions in there. Thank Noejn if you like it.
Download the latest Franco kernel and ZRAM here.
devoid is a Froyo (2.2) rom, so don't get the 2.3 one, get the CFS. Again, read the thread, be sure of what you're getting. Thank francofrancisco if you like it. Donate if you appreciate his work.
Copy all 3 downloaded zip files to your SD card. Don't bother to unzip them, Clockwork wants zips. Once on the SD card, I would strongly recommend checking the MD5 checksums against the ones list in the download threads (currently only devoid). I use QuickSFV on the PC, but you can get MD5 checksum apps for your phone as well. This is to make sure the download isn't corrupt. If you want to use a phone app, you'll need to select Turn off USB storage to enable the SD card again.
Once you're happy, eject the card reader or phone from Windows. Insert the SD card to the phone (if you used a card reader) or press Turn off USB storage on the phone, disconnect the USB cable & turn off the phone.
Use the same process as before to boot into Clockwork. Twice I booted normally, so it can be tricky. Instructions for other phones have mentioned pulling the battery then doing it again. Persevere and you'll get there.
Select wipe cache partition, then Yes. When that's done, select advanced, then Wipe Dalvik Cache, then Yes. Press <Back> to go back to the main menu.
Select install zip from sd card, then choose zip from sdcard. Select the devoid file, then scroll down to the Yes option and select it. This is the main rom, so it'll take a few minutes. When it's done, select choose zip from sd card again and select the franco file, then the Yes option. This should be quick.
At this point it might help to format the SD card. I don't know and haven't done it myself.
Not sure at this point if you need to switch off, then straight back to Clockwork. I booted into the rom following the instructions below and things were fine. Hopefully hecatae will correct me if I'm wrong.
Press <Back>, then select reboot system now. devoid will take a little time to boot. When it's loaded, switch off again, then boot into Clockwork.
Select install zip from sdcard, then choose zip from sdcard, then select the zram file and the Yes option. It'll be quick. Press <Back>, then select reboot system now. devoid will load and you're done.
At this point, you can delete the zip files and clockworkmod directory from the SD card, if you like.
Edited by Celtic67, 08 July 2011 - 10:49 AM.