I am new to the world of HD. How do I tell what my HD signal is. And can a regualar tv display HD signals in lower quality?

I am not sure what you are asking with the 1st question.

As for the 2nd, I have a SD tv that I watch HD channels on.

Your HD signal is coming from your HD cable service or from your HD satellits service and chte HD channel nubers are not the same as the normal broadcast analog channels.
For example on my HD cable service CBS analog SD is channel 2 and CBS digital HD is channel 702. Or possibly you have an HDTV with an ATSC tuner and you are receiving HD digital channels using an antenna connected to it.
Yes all TVs can display HD signals in lower quality by downscaling the HD signal from its source to standard 4:3 aspect ratio 480i resolution

so on a regular tv i can not view an HD channel in the original 16:9 ratio it will put it at 4:3?
thanks

In most cases an ATSC tuner set to output 4:3 will letterbox 16:9 program to retain the aspect ratio. Unless you are receiving channels via OTA or via your basic cable via unencrypted QAM, there is no point in upgrading to HD service for an SD set.

One way to tell is by checking at sources such as http://www.hdtvgalaxy.com/whatson.php for HD program sources and times. Then check whether your local cable system (see the Local HDTV infor and Reception forum here for tips) carries particular HD sources, or ask the cable company about HD service. The same for DBS service. A visit to antennaweb.org, with a zip code or address, provides a list of local HD stations, with other antenna-orientation info for over-the-air (OTA) reception. My HD cable STB displays HD programs in letterbox form (top/bottom black bars) on a 4X3 TV connected to a coax from the STB delivering RF video on a fixed-channel 3. Downconverted video (to 480i SD) looks crisper than standard 480i sources. although the top/bottom black bars means vertical resolution is reduced. -- John

bmp876...all HD is Digital but not all Digital is HD....or am I missing the point completely here...