I was just booting up from the CD to run it and see what it's like before installing
Looks like you've installed it.
feeling rather worried as I didn't back up my data before trying it out...
I'm sorry! Do you really
not know the difference between a live CD and installing by booting?!
Obviously, you're currently installing without a clue!
BTW, Ubuntu's OK. Once you've installed it, choose the menu: "System --> Administration --> Synaptic Package Manager".
From there, install XFCE (or FluxBox).
Press Ctrl+Alt+Backspace to leave your graphical session.
Before logging in again, choose "XFCE" in "Options" at the bottom left on your screen.
... The XFCE desktop takes much less ressources than the - Ubuntu-default- GNOME desktop.
P.S.: To reduce memory hogs, there'll be additional tips, like choosing the web browser or Office tools. - So please come back if there are issues.