A DVD upscaled is HD enough. But yeah I dont understand it either which is why i gave my answer.
OP, do you mean blurays, HD resolution on your monitor...what. HD content in general doesnt help much because there are a ton of ways to do that. Netflix for example, monitor for another, bluray is a third.
First, it depends on whether the HD content is protected or not. If the content is protected, then all of your components need to be HDCP compliant (basically a discrete graphics card and monitor with DVI or HDMI inputs). For non-protected content, you will only need a discrete graphics card installed into your system.
Note: The specifications for your system states a configuration with an Intel Celeron processor. If your system is based on this processor, then it is possible your system is just too low powered to run any HD content.