I wonder if there is a programme that will allow me to say partition a section of my external hardrive and allow an operating system to be installed in that partition so that if I go onto someone else's computer I can run my editing programme off that partition instead of having to install the editing programme on their computer?

Your BIOS must support bootable externals. If it does, Windows XP and Linux can be run from an external, but I would not recommend it for daily use. We built Windows PE (command line Windows) onto a device for this purpose, but it can be problematic at times (using it on multiple machines).

In the PC realm, the device has to be USB. I know that Macs support bootable externals with Firewire, but I have zero experience with it.