Answer: We are not experts in TV arrangements, and not knowing the specifics about your TV equipment and the unit you bought, we really can’t give you any definitive help.
Having said that, our gut reaction is that your old TV isn’t going to be able to support HD. The connectors are different, etc. Even if you can find a converter that will convert HDMI to coax to get things connected, you will not be getting the benefit of HD anyway.
To make sure you get input from someone in the business, we suggest you go back to where you bought the DVD player (or a store that sells these type of products), explain your situation and ask some questions about whether you can really make things work as you might have envisioned. It may be time to upgrade your TV and associated equipment.
Please let us know what you uncover. We haven’t yet upgraded our own old TV. but it is a project we will undertake in the near future. We plan to get a LED HD TV (preferably 3D ready), a DVD player with blue ray, satellite system to support the TV with a DVR, all connected with HDMI cabling.
We have repeatedly put this project off due to budget and changing technology. We want to do the job completely to get the full benefit of HD, etc.
Other input and expertise is welcome!