A preview release of the coming TiVo Desktop 2.4 for Windows is now available for download. If you have a Series3, this includes the promised HD Photo viewer. Photos are now converted to 1280×720 for the S3, instead of being converted to SD resolution (I think the old photo app was 640×480).
2.4 also includes auto-transcode for other video formats into MPEG-2 for the TiVo. The details state that Windows Media (.wmv), QuickTime (.mov), MPEG-4/H.264, and MPEG-2 videos are supported. This feature does require a TiVo Desktop Plus key.
This is a preview release, which puts it somewhere between ‘beta’ and ‘final release’. You can always remove it and reinstall 2.3a if you have problems.