Erratic Graphic Artifacts

[Gregoshi]

I suspect I have a graphics card going bad, but thought I'd throw this out to the more experienced before spending money.

The problem is I'm getting "ghost" (transparent) artifacts from previously displayed items, be it text or graphics. They are teal and/or red in colour and cover most of the screen but are strongest in five evenly spaced vertical columns running down the screen. The problem is very inconsistent. It started about a month ago but I've gone a few days to over a week between incidents. I thought at first it happened only after the PC had been on for most of the day, but this morning it started within 30-60 minutes. Usually a reboot would clear the condition. This morning a reboot cleared it but since then it has twice come and gone on its own over the space of 5-10 minutes, which is a new twist on the problem.

Some additional information:

1) PC (Dell) & graphics card (ATI Radeon 9700) are just about five years old.

2) Right before this started happening, I opened up the case to replace a CD-ROM drive. I didn't have canned compressed air to dust out the case so I used a rubber blower bulb to clear out the dust as best I could. There was still some more stubborn dust on some of the components that I'm sure canned air could remove.

3) I've ruled out the monitor. When the artifacts are on-screen, I can bring up the monitor settings menu artifact free.

Any thoughts? Any additional information needed? Should a good dusting clear it up or am I looking at a new graphics card?