Problems doing a clean install of 10.8

A bit of background first. I bought my first Mac a few weeks back and it looks like the old user left some files behind somehow so I decided to do a clean install of ML. The discussion can be found here - http://www.mac-forums.com/forums/os-x-operating-system/297824-remove-old-user-app-store.html

I have been following the guide on OSX Daily (How to Clean Install OS X Mountain Lion) on how to do a clean install of ML but have ran into some problems.

I got myself a 32gb USB drive, and bought and downloaded the ML app from the app store. I used LionDiskMaker Tool to make the bootable backup of ML. Then I restarted my Mac and pressed Option and selected the USB Drive. I was given a list of 3 options, I can only rememer two of the option were to install a fresh copy of ML, or to erase the data on a drive.

I selected to erase the data on a drive, and was given an option of which drive I wanted to erase, so I selected the main drive, but the erase button was greyed out meaning I couldnt erase it.

I then turned to Google to help, and from what I gather, if I was to boot into the recovery drive, then I could erase the main partition. I wasnt given the option of booting into the recovery partition, and used diskutil list in the terminal and i do infact have a recovery partition. I tried just installing ML on my main partition instead of erasing the data, but this obviously kept all my data intact after reinstalling ML.

I have hit a dead end now as to how to erase the data on my main partition and then install a fresh copy of ML.

Thanks for any help or advice

Also, not sure if it matters, but the USB drive had also renamed itself to 'OS X Mountain Lion Install Disk - 10.8.3' and the size has dropped from 32gb down to 15gb after I used LionDiskMaker. The install file is now no longer visible on the USB Drive but there is still only 15gb free. I presume its hidden itself?

No worries guys, managed to do it by repartitioning hard drive and deleting old partition. Mods - please delete or lock thread...

Glad you got it working.

Just for info if others visit this page:
booting form the USB holding option will display three drives (four if you have a bootcamp partition)
Mac HD / Recovery / USB Installer

A clean install of Mountain Lion, can use, doesn't need the USB drive. You can just do it from the Recovery partition. Having a USB installer means you just have a backup installer in case your drive fails and you can't access the recovery partition.

In either case, once you select either the USB or Recovery partition to boot from you should then open Disk Utility and erase the Mac HD partition. This is a link to a slightly more comprehensive tutorial