I don't think it is a good idea to let your htpc do the 24hz to 60hz as your TV most propably convert much better or even handle 96hz. I'm quite sure motion will be a lot more smooth if you send 24hz to your TV.
The best is to set your htpc with AutoFrenquency. If you are using Media Browser it can also be used with it. See here: http://community.mediabrowser.tv/per...quency-with-mb
This way your HTPC will always switch to optimal resolution / hz for each media.
Personally I'll even switch to 480p for DVD as again my TV is the best choice for upscaling.