first off have never had to use this but have always herd good things about it
The Hiren boot CD
it can be installed to a flash drivehttp://www.hiren.info/pages/bootcd-on-usb-disk
other way might be to get a copy of some thing like http://www.pclinuxos.com/
and install it to the pen drive/flash drive and boot from that
or contact HP for an original disk to be sent out will not be cheep.