Download:Apple lion 10.7
Osx lion gold master 10.7.0
burn to disk using disk utility then boot to install.
Note this is the standard GM Lion and as such this version and all subsequent iterations need an install of snowleopard existing to allow upgrading
to install a fresh simply split ur partition using disk utility select this to install to and then use the migration assistant after install to migrate your old files accross if you like to.
Other Pro Tip
Releasing locked down osx install disks supplied with the latest apple hardware is as lame as they come , firstly they dont work on models of mac below the one bought nor on any other hardware.
Pros never download hotiso releases.
shouts to steve
Apple has released the following basic system requirements for Lion:
Apple Macintosh with Intel Core 2 Duo, i3, i5, i7 or Xeon.
2GB of RAM Memory
7GB Hard Disk Space
Airdrop functionality is supported by the following models of Mac: MacBook (late 2008 or later), MacBook Air (late 2010 or later), MacBook Pro (Late 2008 or later), Mac mini (mid 2010 or later), iMac (early 2009 or later), Mac Pro (early 2009 with an AirPort Extreme card and mid 2010 or later).
Mac OS X 10.6.6 or later (Mac OS X 10.6.8 recommended).
The Mac IA32 Processors such as the Core Solo and Core Duo are not supported by Lion.