And by the way, you might want to look inside the device manager to see what other devices have no drivers installed. They have a yellow (or worse, red) icon next to them.
The Standard VGA Adapter is the generic driver that is included with Windows 7. It doesn't feature acceleration or decode features, so you CAN'T play a lot of videos.
Think of it this way -> Standard VGA Adapter means no proper drivers installed for the video device.
WHY would you want to install windows 7 on a 5100 sff? We recycled about 100 5100sff's and let me tell you 512mb of ram with a Pentium 4 isn't going to run 7 good at all.