From what I know, HDD is used for DVD recorders and stands for Hard Disc Drive. In other words, you can save the record programme directly onto the recorder's hard drive, instead of a disc.
HD TV are high definition televisions because of the high resolutions. There's HD Ready which are TVs with a 768 resolution and "Full" HD with are TVs with a 1080 resolution.
Can't help you at all with the installation of them though.