how good is on board display card on p8z68 v pro. can i play MW3 or cOD 4 on decent settings(not too high with no lag)
No, it would be choppy and slow with High settings and HD resolution of 1920x1080. The iGPU is fine for anything 2D including movies, and pretty much that's about it. Sure some games at mediocre settings - maybe. You can 'try it' and always pop-in a Discrete GPU. I prefer a minimum of 4xAA and only High Quility and minimum Frame Rate of >45FPS for smooth play.
I use sony tv as my dispay with HDMI cable. does this onboard dispaly card capable of Playing game s with HDMI. i m using i2500k CPU.
The HDMI is a Video and Sound cable, IF you get a Discrete GPU then in Virtu you could use the onboard HDMI in I-Mode. However, I find it best to use D-Mode and the 'HDMI' off the Discrete GPU if equipped and preferably versions 1.4 or 1.4a.
Call of Duty:
Here's several comparisons - http://www.anandtech.com/show/4083/the-sandy-bridge-review-intel-core-i7-2600k-i5-2500k-core-i3-2100-tested/11