I am trying to download Ubuntu for PCs (64-bit), but the computer I need to put it on isn't working so I'm trying to use my MacBook, but every time I try to download it I get the Mac version. Does anyone know how I can download the PC version to disk using my Mac?
If it is the 64bit, then it is correct. Unless is says specifically amd64 MAC, then it is correct. here is a link for the 64bit if for whatever reason your computer is not letting you select that http://www.ubuntu.com/download/desktop/contribute/?version=14.04&architecture=amd64
There is NO "mac" version of Ubuntu. It is just "Ubuntu for either i386 (32-bit) or x86_64/amd64 (64-bit)."
Once you have downloaded the requisite file, make sure you have the complete file (check the md5 sum). Then, put it onto a USB stick/thumb-drive using the "longish" procedure outlined here: http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-mac-osx
Take that USB stick/thumb-drive to your "not working" PC and start that PC with the USB stick/thumb-drive plugged in. You should be on your way to running/installing Ubuntu on your "not-working" PC.
(Could you please explain what you mean by "not-working" PC? Thx!)