I NEED MORE STORAGE SPACE!!!! My wife is going to flip out when she finally realizes how much less space there is compared to Directv's DVR's. Does anyone know if we can add an external hard drive??
No, you cannot. Verizon expects to offer more HD capacity / expansion options before the end of this year.
If you need added capacity right now, then you can buy a TivoHD or Moxi. Those are the only available choices for standalone HDTV DVRs with capacity expansion that support FiOS. More information in this post.