Please help me on artifacting on movies

If you have updated your graphics drivers, the next step would be to check your GPU temps. Speedfan is good:

http://www.almico.com/speedfan.php

This is probally a long shot, but what's the monitor your using/TV your using?

Yeah, I couldn't tell you for sure- but if your display drivers are up to date, then I'd go with it either being a badly mastered title or an issue with your monitor. I've actually been working with Warner Home Video on some blu-ray projects and while I've come across a few title with less than perfect images, by and large seeing artifacts (that aren't intentional) is pretty rare.

i have temps on my gpu on mid 40s ... i am using a lcd monitor from lg

Well, I think the only way to rule out the video card at this point would be to use it for something else... if it will play a 3D game fine, then it's either a driver issue or perhaps your movie player.

You'll need to be more specific about your LCD monitor. Model number would be good.

When I'm playing mirror's edge, I get a horizontal line at middle of the screen when I quickly change directions...my lcd is a L227WTG from LG. It says 2ms response time...but why is there the horizontal line?

Could be video memory.

I would say the artifacts and line are likely due to a faulty video card at this point.

I do note that your monitor is not capable of 1080i though... possibly there could be some issues with Blu-Ray titles.

How do you have your monitor hooked up to your video card? Through the vga or the dvi port? If you can (if your not already) hook it up using the dvi hook-up.

If this doesn't work then i'll probally going with proximon saying its either a bad video card (probally its memory) or its your monitor not supporting the HD.

what to do if it's the video card's fault?

RMA, contact the manufacturer, buy a new one. have a few options. Should still be under warrenty if you haven't damaged the card or anything.