Hi guys, I am working on triple-booting my laptop with Windows 7 (already installed), Ubuntu, and OS X ML. I have a fair amount of knowledge regarding PC's and installation, but am completely new to the mac world so please bear with me. I realize I need to have a bootable USB drive to install Mountain Lion (and quite honestly i dont even know if my Dell is compatible... I'll list the specs below). I know this is probably the most tedious part of this process, and with good reason since i've spent 3 days now trying to get this to work.

I have a 32G flash drive i'm going to use as well as the installESD.dmg file verified retail. I have tried creating the boot drive using VirtualBox with snow leopard, however I played around with that a lot and could not get it to work (using the iBoot/Unibeast method). My brother has a macbook pro so I just decided a usb drive would be the same created on that or via virtual box, but probably easier on the macbook. like I said, this part is pretty much new territory. So I have all the files I need on an external HDD. on the mac I go to Disk Utility and reformat the usb drive for macs, and I try to mount the installESD.dmg file, to no avail. I tried using terminal to mount it, i've tried verifying it, i've tried converting it, I've tried restoring it to the usb drive, all with the same message: "The following disk images couldn't be opened. Image:installESD.dmg Reason:not recognized".

so with all that being said, i've eliminated reasons down to two:
1: the file is corrupted and i'll need to redownload it/get a different one
2: for some reason the mac is not recognizing the file and will not mount it.

oh and the macbook is running Lion.

anyways, here are my laptop's specs, I don't even know if its compatible:

Dell Inspiron N5010
Intel Core i3 CPU M 350 2.27GHz quad core
4GB RAM
Intel HD Graphics ("video card")
DW1501 Wireless-N WLAN Half-Mini Card (wireless adapter)
500GB HDD with windows 7 installed, 86.67GB unallocated space for both Mountain Lion and Ubuntu

anyways I've tried everything i could think of and searched the internet extensively and couldn't find anything really relevant to what I'm encountering. any help is appreciated and thank you!

Wrong image file.
I have created my ML usb stick with osx 10.6.8 on virtual machine and when I 2x clic on the dmg SL mount this.
After I have used MyHack for create my usb stick.

You need this also for install osx on MBR partition : link

Now I have 3 boot (Windows 7, Ubuntu and Mountain Lion)