Many thanks for your reply and the help.
You asked for the specs. Here they are.
Motherboard: Pegatron M2N68-LA
Processor: AMD AthlonII x3 64bit 2.7GHz
Graphics Chip: Nvidia GF6150 1407MB
Audio: Realtek ALC662 chip
SATA Hard Drive
Hard Drive: 500GB
OS: Windows7 on a main partition, with a rescue partiton also on the drive. I've made rescue disks, but there's no W7 installation disks supplied
Looking at the motherboard manufacture's site, there is no mention of being able to boot from a USB drive.
Looking in the BIOS, it lists:
1st boot CDROM group
2nd boot Hard Drive group
3rd boot Floppy group (there is no floppy fitted)
4th boot Network group (perhaps a USB drive would appear here?)
For further information, at the moment, I am not allowed to do anything inside the computer.
Can't fit a second internal hard drive as I did in my previous machine, can't fit more memory, upgrade the graphics or sound, can't alter the installed OS to dual boot. That's why an external USB drive is the only answer.
Hope this helps, and thanks again.