wait wait wait...I just re-read that again.... basically you have a video card with RCAs on it? Are you sure those RCAS are inputs and not outputs?
From the ATI website:
At-a-glance
* Powered by the Radeon™ 7200 graphics processing unit (GPU)
* 64MB of powerful single data rate (SDR) memory
* Featuring ATI's Charisma Engine™, Pixel Tapestry™ and Video Immersion™ technologies
* Integrated Transformation, Clipping and Lighting (T&L)
* Accelerates today's top 3D games
* Industry leading video playback
* Supports 3D resolutions (32-bit color) up to 2048x1536
* AGP 2.0 Compliant BUS - AGP 2X (3.3V), AGP 4X (1.5V), or AGP2X/4X based systems
* Video-out option available for European customers
* Designed and manufactured by ATI
* Featuring Catalyst™ - ATI's industry-leading software suite with frequently scheduled free updates providing additional features and performance over the product's lifetime
Thats probably your problem. Those are RCA outputs not inputs. In which case, you have a video card with RCA outputs and not a capture card at all.