I may sound stupid and this probably has been asked before but do you guys think we'll be able to do a clean install?
If a "clean install" is what I'm thinking of it (wiping the whole HDD and install the OS as if it's new) then, yes.
You can either buy Moutain Lion on a thumb drive or download it from Mac App Store.
If you're going the second route, you'll need an USB thumb drive or an empty DVD, just look for "Install OS X Mountain Lion.app" in your "/Applications" folder. Open it (right-click/double-finger-click/control-click > Show Package Content) and extract "InstallESD.dmg" from there by simply copying it to your say Desktop or whatever folder you want to use.
Then open Disk Utility, drag that .dmg into the white blank space. Click on "Recover" tab on make sure, InstallESD.dmg is "source". On "target" specify your USB drive or DVD. Click "Apply" and wait for it.
Boot from the USB drive/DVD (press OPTION/ALT) after the boot-sound and select your drive.
When you're at the "choose your drive to install OS X on it" (don't know what it says exactly, though) open Disk Utility (in Utilities menu) click your current Macintosh HD and wipe it. Make sure your file system is HFS+/Mac OS X Journaled. Close Disk Utility and proceed in installing OS X on that newly wiped partition/drive.
Note: Doing this will cause you to loose all data on the drive (since its's a clean install, we wanted that) and make sure you did a backup first. Not after.
edit1: by the way, I don't know what the menus and buttons are saying exactly since my system is all in German. But it should be similar to what I wrote above.
edit2: Corrected some typos.