Wow, it's just such a thrill to have ubuntu sitting here on a portable drive!!
I just hooked my external drive to the IBM Thinkpad laptop I use for my job.
True, for some reason, I had to install the drive first under Windows XP (I'd expected the BIOS to pick it up right away, but it didnt), but after that, I could boot Ubuntu right away, just like I did on my desktop upstairs.
(Some people might regard it as a bit of a makeshift solution, but I like having the internal hard drive as the default boot device. During startup, I just hit whatever function key BIOS happens to accept to pop up a list of boot devices - F8 on my desktop, F12 on my laptop - and pick my external hard-drive if I want to boot Ubuntu. It makes sense, I really cannot be sure the external drive is hooked up, whereas It's safe to assume the interal hard drive's still there ;-).
So, Ubuntu has just awoken in this strange, new, compact body. From there, I used the graphical "networking" tool to set up my wireless adapter (built-in in my thinkpad, my desktop uses and old fashioned umbilical chord) and lo-and-behold: here I am, sitting in the living downstairs, with my laptop posting this.
I admit, I did reboot once after tinkering with the wireless adapter configuration. It just would not work at once, and the rebooting reflex is kinda engraved in my backbone, being a Windows user since the 3.11 version.
Thanks again Dave (a.k.a. DaBruGo), I really, really am so much obliged to you for posting this solution of yours!! I'll just repeat it here: those that want to have a dual boot solution for ubuntu and they want ubuntu to sit on an external drive, look no further! This thread in the ubuntu forums contains indispensible valuable information. Right, people are even posting replies that tell you how to do this with an USB flash memory stick, imagine that!