For the first driver question, you might want to try Dell's own drivers to see if they change any behavior or anything. The link I found was:
The 4th one down looks like your driver (Radeon X600 256MB).
Sometimes the Dell cards can be a little different from the reference design, and while this is likely NOT the case for you (i.e. the AMD drivers should work fine), it's worth trying these to see if they work better for you.
On your second issue with moving the PC = colors... it sounds like you either the connector on the card/monitor is loose or the cable is going bad. Does the cable screw-in to the monitor or is it permanently attached? If it's screwed-in, you can likely try replacing the cable to see if this fixes it. If not, try switching with another monitor to rule out a bad cable/cable connector.