iBoot ivy is to allow you to use a retail OS X Snow Leopard DVD to install SL and get to the app store to download ML without doing any post install fixes in SL to allow it to boot. What you do is:
1. Install SL with iBoot Ivy+ SL retail DVD
2. At SL desktop, forget about running MultiBeast. Go straight to Apple support and download the 10.6.8 Update (combo)
3. run 10.6.8 combo updater and reboot with iBoot Ivy
4. at desktop again, click the App Store icon in the dock, log in at the App Store - if you don't have an Apple account, (you should have one) then register for one
5. Purchase and download the Install OS X Mountain Lion.app from the App Store.
6. It puts the Install..app in your app folder.
7. Download the UniBeast app from the forum downloads.
8. Format your UniBeast USB and create your UniBeast USB installer - see
http://www.tonymacx86.com/61-unibeast-install-os-x-mountain-lion-any-supported-intel-based-pc.html and install ML on your PC.
Note: I found if you use the 10.6.7 update combo, you could download Lion, but that might be because I had already purchased it previously. I would be interested to know if you can get Lion this way if you have never purchased/downloaded it.