evga 8800GTS problem in Civ4-BTS

I have Civ 4 Complete (UK version includes both expansions) running on my US Windows XP install. Overall, I have no issues. Seems to run great. But I have noticed just one thing. It is related to those light colored latitude lines that pop up occasionally.

Anyway, instead of just being light colored they end up being multi colored and are expanded in width and clearly not the luminous white color they are supposed to be. Last night I had one that was mixed colors of mostly red and black and was roughly the width of one square in the grid.

Here's some info on my system:

Intel C2D E6750 | Gigabyte GA-P35-DS3R | eVGA 8800GTS (320) | LG L206WTY 20" Widescreen LCD | Corsair 520HX PSU | 4GB RAM (only 3.5 recognized) | Windows XP Pro SP2

The card is about 11 months old...I purchased it around the end of August last year I think.

I have 2 screenshots showing the problem here:
http://picasaweb.google.com/trimicada/Civ4ScreenShots

Editing to say: the problem goes and comes. It goes away whenever the lines are supposed to go away and then re-occurs the next time those lines appear and does seem to get worse the longer I play.

I guess that does make it sound like the problem is the card, but why would ONLY the drawing of the lines be the problem?

Guess I need to go see if I registered my card at eVGA or not after I bought it.