After digging around quite a bit, I've answered my own questions.
1: MultiMC(here) allows for multiple minecraft versions to be used on a single machine
2: Minecraft 1.4.7's .jar file can be found here.
As I was having trouble sorting out how to get it all to work, I'll explain the steps I took:
1: download both MultiMC and MC 1.4.7 jar from above.
To get MC 1.5.01 working with MultiMC
1: Save MultiMC somewhere you want all your minecraft instances to be
2: Start MultiMC
3: Click the top left icon: Add New Instance
4: Click "OK" when the error pops up. It basically says it couldn't determine the lastest version of MC
5: Enter the name you want to call your first instance(this will be 1.5.1) and click the "OK" button
6: Double click the new instance, which will download and run the latest version of minecraft(1.5.1).
7: Once minecraft has started, close out of it.
Once finished with 1.5.1, time to do 1.4.7:
1: Navigate to where you saved MultiMC to
2: Open the instances subfolder in your MultiMC directory
3: Create a new folder (This will be your 1.4.7 instance)
4: Open the 1.5.1 folder and copy everything in it(including subfolders)
5: Navigate to your 1.4.7 folder and paste what was copied from your 1.5.1 folder
6: Open the instance.cfg file that is now in your 1.4.7 folder with a text editor and replace its contents with