It wont be other apps running as it does most of the work on the graphics card unless by other stuff that would be a game, benchmark or something - basically you would know.

The test app should be rendering at about 500 frames per second. Not that you would see all those frames but the test app is supposed to say its too slow if its about 50 frames per second or slower. At the end it shows the framerate. On the very top line it says for me...
"OpenGL is successfully running this application with hardware assisted graphics acceleration".

I suspect that it is saying something different for you. Its probably saying that its using the built in software renderer which would be much slower - like 20 frames per second. In the directory that you run the test there is a file called TestResults.txt which you can get at with notepad. The top half of mine says the following...

Code:
OpenGL is successfully running this application with hardware
    assisted graphics acceleration.

Card Vendor / Renderer: GeForce 8600 GT/PCI/SSE2

OpenGL Version: 2.1.2

ViewingDale needs at least version 1.1.0 so this looks good.

Frames rendered: 13433

Frames per second: 447.8

Your system is sufficiently fast enough to run ViewingDale effectively.
if your able to post that bit then we can see what is going on with your system.