After research I discovered that I could do this by changing the BIOS settings but there doesn't seem to be "USB boot" option there. I updated the BIOS to the latest version (PhoenixBIOS 4.0 Release 6.0, Version: 0F0A ) but I still don't have that option.
Is this a problem with the motherboard (HP 311282-001), the drive (LG GSA-2166D) or something else?
By the way I'm running Windows XP Pro on a Compaq Evo n1020v.
Any help would be really appreciated.