Do You Have to Have HD for the HD DVR to Work?

We initially had set up our service 6 months ago with an HD DVR in anticipation of purchasing a new HD tv. Due to some unexpected bills, we won't have an HD tv until the holidays, so I'm wondering if I disconnect the HD programming, will the HD DVR still work?

DTV is being sucky about giving us free HD for Life, so why should I give them an extra $10 per month for something we're not currently using.