Distorted, Garbled, Jumpy lcd on Mac Book Pro C2D 15

I have tried look through other threads and couldn't get to the exact issue so please pardon the information here if it is redundant to some.

Here is the issue:

When I connect the DVI to VGA connector to an external monitor or overhead projector everything is ok for a few minutes and then the LCD starts to scramble, distort, garble et all.

If I disconnect the DVI dongle the screen will settle enough for me to see the Blue apple to shut the system down and restart.

Restarting is the only way to get the video back to normal.

This is an issue as I present a lot. To date, I haven't been able to depend on this unit to perform this activity.

Do any of you have any suggesstions?

Thanks,
Jamie

MacBookPro Mac OS X (10.4.8)