Which version of Windows will run on an iMac 24" early 2009 model? I have an iMac 24", early 2009 model with 2.66 GHz Intel Core 2 Duo and 4 GB RAM running OS X Yosemite.  I need to setup my Boot Camp and have done a lot of research, learned a lot but still unsure on a couple of points.  

Based on my iMac's hardware, Microsoft tech support recommended the 64 bit version of Windows 8.1 Pro.  With Boot Camp Assistant 5.1.3, I tried and kept getting an error message that my Boot Camp only support Windows 7.

I did see that on the Apple's Boot Camp Support site, my iMac model can only run 32 bit Windows 7.  However, on the EveryMac.com, it stated that some users reported success in running the 64 bit version with the correct drivers.

So here's my questions:
1.  Which drivers are they talking about?
2. Is my version (5.1.3) of Boot Camp Assistant the wrong one to use and that's why it failed to install the Windows 8.1 64 bit version?

Ultimately, I like to know which version of Windows (7 or 8, 32 or 64 bit) can I successful install using which version of Boot Camp Assistant?

I'd appreciate any suggestions or advices.
I managed to install Windows 8.1 Pro on my early 2009 24 inch iMac yesterday. Just a disclaimer: I DID NOT USE BOOT CAMP ASSISTANT TO INSTALL. For 2 days straight I troubleshooted boot camp assistant to try to get it to take my Windows 8.1 Pro to no avail. Out of frustration I googled 'how to run windows on a mac WITHOUT boot camp.' After finding a guide online, in a matter of about 30 minutes I had successfully installed Windows 8.1 Pro on my 2009 iMac. Here is the link to the guide....you can ask me any questions regarding this. 
See "How To Install Windows 8.1 On Mac Without Boot Camp".