Hello and welcome to AskUbuntu! Good for you for being open to discovering the awesomeness of Linux!
For convenience, here's a direct link to the Kubuntu x64 ISO
FYI: The 64-bit version has "AMD" in the name simply because AMD created the modern x64 architecture as we know it. I think Intel still leases x64 from AMD...
You do not need a Mac-specific image, and you definitely want the x64 version.
Backup, backup, backup!
No matter how many people have successfully installed Ubuntu alongside OSX, there is still a very real possibility of losing everything on your hard disk, so please, do the prudent thing and make a full backup before proceeding!
Note: You need to install rEFInd to get a boot menu on startup.
Here's a guide on how to do that, taken from the How-To-Geek:
rEFInd is a boot manager that will allow you to choose between Mac OS
X, Linux, Windows, and other operating systems when you boot your
computer. Installing rEFInd makes the dual-boot process easier. (Some
older how-to’s will instruct you to use rEFIt, but it’s no longer
maintained. rEFInd is a currently maintained boot manager based on
rEFIt.)
Full-disk encryption causes problems with rEFIt, so you’ll need to
disable full-disk encryption or do some extra work before installing
rEFInd.
First, visit the rEFInd page on SourceForge and click the Download
button to download the latest refind-bin-[version].zip file. Open a
Terminal window by pressing Command+Space and, typing Terminal, and
pressing Enter. Drag and drop the install.sh file from the downloaded
zip file into the terminal window and press Enter to run it.

Shut down your Mac — a full shut down, not a restart — and boot it
back up again. You should see the rEFInd boot manager screen.

Now for the actual install:
While the ISO is downloading, use Disk Utility to partition your HDD. Make sure to leave the partition you create as "Free Space". (No filesystem)

After you download the ISO, burn it to a blank DVD.
If you'd like to burn it to a USB stick instead, see: https://www.ubuntu.com/download/desktop/create-a-usb-stick-on-mac-osx
Next, hold down the Option key while hitting the power button. Continue to hold it down until you get the boot device selection menu. Then you want to choose "EFI Boot". It will show a picture of a DVD if you burned it to a DVD, and it will show a picture of a drive if you burned it to a USB stick.

After the installer loads, select the "Install Ubuntu" option, and then select "Install Alongside Mac OSX". Hopefully, it will automatically install to the partition you left as "Free Space" earlier.

After it installs, shut down and remove the installation media. Then reboot, and cross your fingers. Hopefully you'll see this:

If after installing your Wi-Fi doesn't work:
Then you should post a new question on this site, including the version of Ubuntu you installed, whether you have a working Ethernet port, and the output of these two terminal commands:
lspci -nnk | grep 0280 -A2
rfkill list all
And I'm sure Pilot6 or Chili555 will be glad to assist you! Make sure you add the wireless tag!