Many thanks for all the suggestions and assistance.
I couldn't work out how best to give a report back of how I got on, so I'm writing it as an "answer".
It took all of yesterday evening and through the night chugging away, but I now have 12.04 LTS running and working perfectly on my eight-year-old little Samsung laptop (of which I'm very fond, despite its rather feeble processing power). I am due to treat it to a brand new hard drive as Ubuntu warns me that its current one is about to cark it.
Here are the steps it took to get 12.04 LTS working on this non-PAE machine:
- Installed 11.10 again from scratch using the option to completely remove 9.10 and replace it
- Installed all the updates via Internet
- Took up the offer of downloading the upgrade to 12.04 LTS over the Internet
- This ground to a halt due to the 6GB of disk space being all used up
Bah. I did not want to eat into the Windows XP partition, and didn't see why I needed more than 6GB of disk space just to have Ubuntu for general web browsing and checking emails, so I started again:
- Installed 11.10 again from scratch using the option to completely remove the knackered 12.04 LTS install and replace it
- Did not install any of the updates
- Removed a load of programs and applications from 11.10
- Tried again to upgrade to 12.04 LTS via internet connection
- Disk space ran out again and installation had to be aborted
I tried looking at how the disk was partitioned, and there were about four partitions in addition to the XP. I rather blindly and haphazardly deleted all of them except for the XP one and a ca. 300 MB swap partition, and created a new one for the Ubuntu partition with the number "4" and a single "\" or "/" involved in it somewhere. I was sort of past caring (and losing the will to live) by that point and was crossing my fingers that my XP partition wouldn't be trashed.
At that point I also read that before upgrading to 12.04, you should update all software on the existing [11.10] release. (So my ploy of deleting loads of programs would have come to naught). I also discovered the link to the alternative CD iso file, so burned that to a CD rather than using the internet (even though the internet connection is faster than reading from a CD at 70MB/s thanks to a recent free BT [British Telecom] upgrade). My reckoning was that I could preserve disk space by using the CD because the more recent updates wouldn't be downloaded during the installation.
So, onward, I tried this:
- Installed 11.10 again from scratch using the option to remove the incomplete 12.04 LTS and replace it
- Installed all the suggested 11.10 updates via internet connection
- Rebooted, removing wired internet connection and switching off wireless
- Upgraded to 12.04 LTS offline using alternative CD (left it chugging away all night)
- Rebooted in the morning
- Downloaded and installed updates via internet
And hurrah! It now works (as does booting to Windows XP, phew), without a single glitch or incompatibility. I'm very impressed that all the Fn key combinations work, the wireless works, the screen looks great, and the speakers can be made to have their volume much louder than in Windows (meaning I don't have to use headphones most of the time to hear anything). I can even scroll up and down using the right-hand edge of the touchpad without having had to enable the feature! Plus, the hard drive doesn't grind away incessantly as has become the case with Windows. I love the Ubuntu font and, again, the outstanding readability of screen text on Ubuntu (noticeably better than Win or Mac in my opinion). Having the launcher at the left of the screen I wasn't too keen on at first glance, but having read the reasoning behind that design choice, it's something I'll try to get used to. It sensibly uses the abundant horizontal space to free up some of the much more scarce vertical space.
I'll end the gushing and waffling here with thanks again to everyone for their advice. I hope this description of my trials, errors and eventual success is of use to someone!