I have a Nexus 7 (wifi) with Multirom. I can install a .zip Rom or a Ubuntu image whithout wipe the data and Boot one or another.
But I don't know what image have I to download from your download page.
Can you help me?
You will need to follow the steps as detailed in this post: http://forum.xda-developers.com/showpost.php?p=38300214&postcount=104 .
Quoting the original post:
Requirements: You'll need MultiROM installed with recovery from at least 22nd of February. You can find downloads and installation instruction in in MultiROM's thread (post #2 on this page: http://forum.xda-developers.com/showthread.php?t=2011403), as soon as you have it all installed, come back to this post. Free space needed: a little over 1 GB.
Downloads: You'll need two ZIP files from this daily build page. a) Base system: raring-preinstalled-armel+grouper.zip (~32 MB). b) Ubuntu data: raring-preinstalled-phablet-armhf.zip (the biggest one, ~372 MB)
Installing base: Reboot to recovery and got to Advanced->MultiROM. Select "Add ROM" option. Choose these settings: a) Choose ROM type: Android/Ubuntu touch. b) Share kernel with Internal ROM: Don't share. c) Install location: Wherever you wish to install it. Click Next, then select ZIP file as ROM source, and choose the smaller ZIP file with base system (raring-preinstalled-armel+grouper.zip). Proceed with installation. Do not reboot after installation! Installing on USB: if you get to screen which wants you to "Set up the size of disk images", set the size of data.img to something bigger - 1500mb should be enough.
Installing Ubuntu data: Select List ROMs in MultiROM menu in recovery, then select the ROM you've just created (probably named something like Ubuntu_Touch...) and choose Flash ZIP option. Select the bigger ZIP file (raring-preinstalled-phablet-armhf.zip) and flash it. Beware, this ZIP file then can't be used to flash Ubuntu without MultiROM, as it is modified in the process to suit MultiROM needs.
Profit: Ubuntu touch developer preview is now installed. Keep in mind that this really is just a preview, so pretty much nothing will work. Looks good though.
Its very very easy all you have to do is make sure you are unlocked and rooted.
THATS ALL!!!