You cannot upgrade from XP OR VISTA with Windows 8.1
You must have VISTA SP1 and VISTA SP2 installed to upgrade
from Vista Home to windows 8.0 or Vista Business to Windows 8.0 PRO.
Watching DVDs requires a separate
Windows Media Center license update pack.
To install 64-bit WIN8.1 on a 64-bit PC, your processor and BIOS
must support PAE, NX, SSE2,CMPXCHG16b, PrefetchW, and LAHF/SAHF
Client Hyper-V requires a 64-bit system with
second level address translation (SLAT)
capabilities and additional 2 GB of RAM
Graphics card:128 Meg RAM Microsoft DirectX 9 graphics device
with VISTA32 or VISTA64 WDDM 1.0 driver
Using Directx9 drivers requires the June 2010 Directx patch.
http://www.microsoft.com/en-us/download/details.aspx?id=8109
You download and extract into folder then run DXSETUP.EXE