Step 1 - Buy external HDD.
Step 2 - Partition External HDD to have a small unformatted partition, and a large unformatted partition.
Step 3 - Install Linux on the small partition using an ext4 filesystem, and then format the large partition with NTFS from within windows.
Step 4 - Boot from your external Hard drive on your home computer and set up everything you want on your desktop.
Step 5 - Take your external drive around to a friends house. Edit their BIOS to boot from your external drive.
Step 6 - Enjoy your own desktop, with all your tweaks and settings, fully functional, on your friends computer.
Step 7 - Set your friends BIOS back to the way it was before you came around, so they can get back into their computer.
Step 8 - Leave.
In a nutshell, what this lets me do is use an external hard drive as the root of any computer system. All my tweaks and programs are readily available. I don't have to figure out where anything is on a friends PC (With some messy friends this is a nightmare), and on top of that, if you're using a friends PC who doesn't know how to take care of their stuff, you don't end up getting suckered into fixing their spyware problems!
Everybody wins! Its also safer all round than using your friends PC, since if anything goes wrong and you screw up from within the linux on your hard drive, the only thing that'll get screwed up is your linux partition on that hard drive, rather than your friends computer.
I know, nobody cares, but I thought this was a cool idea
I've also tested it, and it works just fine!
For anyone who is wondering why I didn't install windows, heres why - Windows tracks the composition of hardware in a system. If you change too much hardware at once, windows throws a fit and assumes you've cloned the hard drive to use in another computer, and won't boot, as an anti-piracy measure. It wouldn't work!