What devices will work?
The reason things work so well in theory is that they all support DLNA standards for sharing content on a network. You right click a piece of content in Windows Media Player, select "Play To..." and up pops any and all devices that can be commandeered. The good news here is that any media "renderer"?be it a networked photo frame or a PS3?that ends up supporting the standard will be able to receive anything you hurl at it from your Windows 7 box, and you'll even be able to grab content from servers and other computers and play them on the renderer of your choice. The downside is that there will surely be good products that don't support the spec for one reason or another..
The thing to do now is to ask directv if their hr24-500 supports it. If it doesn't, ask when they will be offering a firmware update. If it does in principle, ask why it doesn't with you.
Please let us know the outcome of your enquiries.