Booting from a USB

[Wendelspanswick]

I downloaded Rufus, followed the instructions, plugged it into the laptop and it still didn't detect it. Then I did it again so I could take a picture of the BIOS menu to ask if I'd done it right and this time it decided to work. The crappy old Acer was no faster though.

You could try the Raspberry Pi's OS, Pixel:

On a side note, the OS can be used to restore an old computer to its prime because PIXEL is suited best to running on older PCs that are too slow to run modern operating systems. Another plus: PIXEL comes bundled with an office suite, a browser, educational games and programming tools that you would find on Pi but exclude Minecraft and Wolfram Mathematica due to licensing reasons.

 

[MrFluffy]

Or a lightweight linux, instead of adding a layer of java onto a linux kernel and making it even worse (android...) or having user friendly hand holding everything with gui all singing all dancing super friendly linux (mint,ubuntu etc). I haven't ran pixel myself but as I understand it, its targeted at people who want to develop stuff targetted to run in a raspberry pi distro, not a lightweight distro in itself, anyway :-
https://en.wikipedia.org/wiki/Lightweight_Linux_distribution

I personally have ran dsl on a router, and bodhi on one of my old android tablets, both are fine along with all the other choices on that wiki page. I used to be a maintainer of a page on how to run gentoo on a windriver netbook and that was tiny, low spec and performed just fine. I'd still use it today but I could never get my fingers trained to the netbook 3/4 keyboard as I'm flitting to real size keyboards all the time.
Once upon a time a pentium was a decent spec machine and they managed to run desktops and browsers etc under linux just fine before all the bloat came along.

 

[bump]

I downloaded Rufus, followed the instructions, plugged it into the laptop and it still didn't detect it. Then I did it again so I could take a picture of the BIOS menu to ask if I'd done it right and this time it decided to work. The crappy old Acer was no faster though.

Ah in that case try taking Lubuntu for a spin. Now you've got the process down should be easy.