http://support.amd.com/us/kbarticles/Pages/catalystlegacywin8.aspx
This AMD CatalystTM driver version features Windows® 8 support for the AMD RadeonTM HD 4000, HD 3000 and HD 2000 series. Please note that the driver is not Microsoft® logo certified and only supports WDDM 1.1 driver level features.
The bolded portion would be the why, and most likely you won't be able to. I would suggest sticking with Win7 as it will do absolutely everything you need + the added benefit of full driver support. 
-------------------------
The opinions expressed above do not represent those of Advanced Micro Devices or any of their affiliates.
Requiescat In Pace AMD Processor Forums | Member since: 1/19/2009 | Post count: 4142
Please don't PM me with questions, instead create a thread so that everyone can assist and benefit from the knowledge provided. Thanks in advance!