Smearing in areas - Video Card or Monitor?

I've just built a box with a GeForce 8800 GTX graphics card and a 20
inch Videoseven monitor running at 1280x1024@60Hz. The connection
between the two is unfortunately via D-Sub not DVI.

My issue is that the I can see obvious 'smearing' of text in a browser
or document- It occurs in certain areas of the screen only, i.e. if I
move the window with the text slightly, a different bit of text will
become smeared.

Is this likely to be a videocard or monitor issue, and how would I go
about troubleshooting? I can't see any obvious smearing in full-screen
games for instance, which makes me wonder if it's the card.

Thanks in advance!