green line across the screen

I have kinda of an odd problem, when I run civ 4 there is a green line that is horizontal across the screen...it moves up and down a little bit, but generally stays in the middle of the monitor....the rest of the game runs fine as far as I can tell, I've tried altering settings but to no avail...the green line shows up from the main menu and is still there for the game, but not in the intro screens. Here's my system specs

AMD 3000+
2 Geforce 6600 gt's w/ SLI
512 mbs ram
200 gb hd
windows XP
I have all the latest drivers and updates of everything.

h n/m

search is my friend

This should do the trick for you

Right click on the DESKTOP
Left click PROPERTIES
Click on the SETTINGS TAB
Click on the ADVANCED BUTTON
Click on the NVIDIA GEFORCE TAB
Along the left hand side should be an option for NVIDIA SLI, click on this
Untick the box for SHOW GPU LOAD BALANCING
Click APPLY
Click OK