1. Find your motherboard manual. This will be included with your computer when you purchased it if you purchased from a retail chain or available for download from the manufacturer's site if you purchased used or from a local BTO store. (sometimes it's included on a CD as a txt, doc or pdf file) 2. Find out from the manual what sort of interface you have for video cards (if any). These will range from; a. None - (on-board video only) b. PCI - (older boards / not made anymore and difficult to find cards for) c. AGP - older but still being made / comes in various speeds... AGP/x2/x4/x8. Higher speeds are backwards compatible with lower on all computers (except x8 on Macs). d. PCIe (or PCI-X) - newer interface and most common in new machines e. PCIe2 (or PCIX2) - newest interface and will accept PCIe cards. 3. Once you have established what interface your motherboard uses then you just look for the interface info on the video cards you are looking at and compare. It will be on the outside of the retail box under the "System Requirements" heading or somewhere in the "Detailed Specifications" area of the page at an on-line retailer. Hope this helps.