Sony Display Laggin

[amdownzintel]

Hi, hooking up an HP computer to a Sony 60" TV and well trying to play Hi-Def videos through it and it's lagging no matter what resolution we put it at. We bumped up the video card in it and put an X800XL, Creative Xi-FI-Platinum Sound Card in it and it already has the X24200 in the guy. So I really don't think it has problems with the hardware is there something I'm missing here? Also it has a gig of ram. The connection to the TV is one cable it's going DVI to HDMI on the back of the Sony screen. The Sony is a KDSR60XBR1

Link for TV = http://www.circuitcity.com/ssm/Sony...31142/catOid/-12870/rpem/ccd/productDetail.do

Thanks!