How do I install Ubuntu on Windows, from a Mac?

Not sure if the title is specific enough, so here we go:

I crashed my Windows pc, and now I want to install Ubuntu on that computer. I'm currently using my Mac, as it is the only operable computer I have left. I have downloaded the .iso. I guess my question is; How do I go about installing Ubuntu on my crashed computer from the external harddrive? I've used Ubuntu before, but I used to install it from a CD-rom. I tried reading the instructions, but couldn't really understand them. Please help

Edit: As Tom mentioned, I only want to install Ubuntu on the (formerly) Windows machine. Anyways, thanks for the quick responses, I think I've got it from here. Cheers

I'm going to assume you want to install Ubuntu only on the (formerly) Windows machine. If you want to keep Windows edit your question, as this changes things completely. Either way, I hope you backed up your data prior to the machine crashing.

From your Mac, you need to make a LiveCD or a Live USB to use to install Ubuntu on the other machine. Official, comprehensive instructions are at those links.

Once you have a Live CD or Live USB, go ahead with a standard Ubuntu install on the second computer. This is pretty straightforward and the Ubuntu.com site has instructions here.

This won't be too complicated so don't worry. If you get stuck, keep notes on what step you are stuck at and edit your question with the new details. Good luck.