There are 2 brands of set top boxes and dvr's.  It depends where you live as to which one you will get.  In the Dallas/Ft worth area they use the Motorola boxes.  Other places they use the Cisco boxes.  Where I work, we install the Cisco boxes so any information I have will be on that standard.  If you are getting HD installed on your order, you should get the high capacity DVR.  The only difference between the standard and high capacity DVR is the size of the hard drive.  Standard dvr's use a 160 gb hard drive.  The high capacity dvr uses a 320 gb hard drive.  They both have the same connections and support the same services and standards.  They are almost identical with the only difference being the model number on the outside of the dvr box.  Be sure to ask your installer about it since they are the ones who install all of the set top boxes and dvr's.