chostetler: A 720p video file with lossless or uncompressed encoding can have a data rate of 80-100 MBs per second.
Most hard drives can't keep u p with such a high data rate and that's why the video file skips frames so badly when you attempt to play it back. People who need to play back such files often use RAID levels in which multiple hard drives are stripped together and formatted as a single volume to obtain that kind of sustained speed.
Many users use these uncompressed or lossless files as a master, from which they produce distribution versions with aggressive compression for different needs. You feed your master file to a dedicated encoding application (such as Adobe Media Encoder). These encoding applications don't require to play those files in real time for full frame rate playback (encoding happens way more slowly), so they the high data rate is not an issue.
In any case, you can export your file as 720p HD, but using compressed formats, like H264, or using lossy codecs in Quicktime (like Photo JPEG) or AVI files.
The default Lossless render setting is just that - it always generates an uncompressed movie, whose data rates at HD res are way too high to be played from normal hard drives. As explained, you need to work with a compressed format. For more info on that, check the Basics of Rendering and Exporting section of the help file. It also provides info regarding your missing audio.
thanks that worked perfect. you guys are awesome and a quick help!