SUCCESS: Imac 27" Late-2013 Bootcamp to Windows 7

Question

After one grueling day fighting with possibly every Bootcamp-related issue there is, I have finally installed Windows 7 on my brand new shiny iMac 27".
I have these threads to thank:
Boot Camp - Setup was unable to create a new system partition....from Windows install
1 Billion Other Threads on "Downloading Support Software"
Here's the story so far:
The first problem was Bootcamp hanging forever on 'Downloading Support Software'. This could either mean my USB wasn't formatted right, or my connection was slow period (it wasn't). Many threads advised to manually download Bootcamp 5 software instead, but they failed to explain what should I use it for. How am I supposed to run and install this, when Bootcamp Assistant can't even install Windows in the first place? I was an octopus flailing in the dark, with so many questions but so few answers, some which were clearly over-tech for me to implement.
Then, at the stroke of midnight, after combining solutions I read in many threads, I have came up with a single dummy guide which I hope is useful to everyone who's hating Bootcamp right now.
Note: This is for iMac 27" Late-2013 (Low end Spec), Yosemite OSX.
Things You Need:
1. BootCamp5.1.5640 (If you're using a different model, refer to table here.)
The idea is to "manually" download the files that Bootcamp Assistant couldn't, which is possibly why it was forever stuck on 'Downloading Support Software'. The manual part, I understood - what nobody explained, was what to do with this file after. So here was what I did:
After unzipping all the files into a single folder, I compressed them again into a DMG file, using Disk Utility. (New > Disk Image from Folder)
The file is then renamed as 'WindowsSupport.dmg". After this, go to YourMac/Library/Application Support/Bootcamp/ and drop the DMG file there. Make a backup of the Bootcamp files, as you don't want to download it again. (Thank you, Loner T, I see you everywhere, you were my saviour in this one).
2. A 8GB USB Stick or Ext Hard Drive
Here's something you should know before installing:
Windows 7: A 2.0 USB Flash Drive or HD, 2007 or earlier model. (The reason is because Windows 7 is not compatible with 3.0 USB sticks, which came out post 2008.) 8GB or higher.
Windows 8: Any 2.0/3.0 USB Flash Drive or HD, 8GB or higher. (Based on sources).
I wish someone had pointed this out to me earlier before I rushed out and bought a Kingston Traveler 3.0 USB. Le sigh. Well, now that you know, you can breathe a little easier knowing that you just saved yourself a potential issue + 4 hours of frustration. In the end, I managed to locate my sister's old HD (I used an old ext HD, 2006 model), deleted everything and will naturally apologize later.
1. REMOVE ALL USB/HD except for the one you're gonna install Windows on. Apparently, this is important as it'll avoid some glitch.
2. Open up Disk Utility, and erase/format your USB to FAT.
3. Open up Bootcamp Assistant, and check all three options. You can never skip 'Downloading Support Software' anyway.
4. BA will load, and when it hits 'DSS', it will prompt you for a confirmation to enter password. This will trigger that "WindowsSupport.dmg" file you just placed in the folder (it will disappear, and until now, I have no idea why. But apparently, it works, because for the first time, there was progress.) It sped up my download bar, although I still had to wait a bit. After a long while, it will proceed with SAVING SUPPORT SOFTWARE, and this is where you celebrate.
5. Go through the rest of the steps, and Mac will reboot, this time, with Windows Installation.
Windows Installation (Windows 7)
1. Click Install Windows Now.
2. You have the option of Upgrading Windows or Custom (Advanced) Install. Click Custom Advanced, then format Partition : Bootcamp.
3. This is where you pray : You either proceed with the rest of the installation, OR, you get stuck with 'Unable to create system partition...' Have a look at the thread above for solutions. I didn't run into any problems whatsoever.
You should be able to take it from here.
Considering that this whole process nearly made me vomit blood, I am so so happy at installing this, I think I may have been channeling my inner geek girl. HOORAY!!!
EPILOGUE: I have also successfully installed my PS3 Dual Shock Controller, and now, I'm playing a heck lot of Windows games on my Mac like a happy fangirl. It's ON!

Answer 1

Thank you for posting your success story and a concise guide. Glad to see another happy user.