This will show you how to burn the downloaded osx lion to a usb flash drive so that you can do a fresh install.
- download lion from the app store.
- right click the downloaded file
- click ‘show package contents’
- go to contents > sharedsupport
- right click on the installesd.dmg
- copy it, and paste it on your desktop
- insert flash drive [8gb recommended]
- open disk uility
- click on your flash drive in the left column and click ‘erase’
- dont do it on your harddrive.
once the usb drive is erased and formatted [as a mac partition]
- drag the installesd.dmg to the left column of disk utility
- then click on it in the disk utility
- goto restore
- as source drag the installesd.dmg to that box
- as destination drag the freshly formatted usb drives partition
- hit ok.
enjoy your lion install flash drive :D