I can't boot ubuntu from Usb flash driver (8Gb) from Windows xp .. Is there any Autoboot or something like that . Can you answer that now cause My Pc is messed up with virus i want to install that now
Then You need to open BIOS to configure boot order and choose USB disk as first bootable driver to boot from it.
BIOS generally opens with speical key like F2 / DEL. At is also shown in the splash screen of BIOS if available.