Advice for desktop purchase

I will be taking an overseas assignment soon and want to set up a Slingbox in the U.S. in order to watch programming from home. I would like to buy a refurbished/lease return desktop on the cheap and install a dedicated video card just for tv viewing. Can someone recommend a computer and the proper video card for it? I have listed Slingbox's minimum computer requirements.

Thanks

Windows® or Mac® Minimum Requirements
• Intel® Core™ 2 Duo or better
• DirectX 9 Class video card with more than 256 MB of dedicated memory for Windows PC
Operating Systems
• OS X 10.7.x or later
• Windows 7 or later (Windows 8 in desktop mode only)
Browsers
• Latest versions of Chrome™, Firefox®, Internet Explorer® or Safari® (OS X only)