A basic overview is D-STAR is a Digital Mode for Voice & low speed data (name, callsign, location, etc) on 2m, 70cm and 23cm, and also High Speed Data (128Kbps) on 23cm only.
You can use D-STAR either in Simplex Mode, or via Repeaters or Links (most of which are internet connected). The Web connected Repeaters & Links can be connected to Reflectors (conference rooms) where communication around the world can take place. Chris mentioned that Reflectors REF001C (US) & REF005A (UK) are quite popular depending on time of day.
D-STAR users can also make use of DPRS (a D-STAR version of APRS) and send GPS data via the Links & Repeaters which is turn is feed to the internet (see GPS Mapping link below).
At the Moment Icom is the only manufacturer of D-STAR radios and these tend to start around the £350 price mark. The Programming Software & Cables, GPS units can be included or separate add ons which will cost more, and older radios which maybe “D-STAR Compatible” might need an additional add on board to work this mode.
Here are a few Dstar web links Chris sent to post on the webpage:-
Reflector 1C live audio stream – http://www.radioreference.com/apps/audio/?feedId=1647
South Yorkshire repeater group dstar “shack cam” – http://www.southyorkshirerepeatergroup.co.uk/tv/gb7yd-tv
Bromley repeater group – http://www.gb3ok.com/gb7ok_homepage.html
Wikipedia article on Dstar – http://en.wikipedia.org/wiki/D-STAR
Ambe chip manual – http://www.dvsinc.com/manuals/AMBE-2020_manual.pdf
DStar UK Yahoo group – http://groups.yahoo.com/group/dstar-uk
Article on GMSK modulation – http://www.scribd.com/mobile/documents/16190764/download?commit=Download+Now
DStar Tutorial – http://www.napasars.org/news/Mar09/Dstartutorial.htm
Icom dstar page – http://www.icomuk.co.uk/categoryRender.asp?categoryID=3786
DStar repeater directory – http://dstarusers.org/repeaters.php
GPS mapping site – http://aprs.fi/
Dstar DV Adapter – http://dstarradioclub-international.com/DstarDVAdapter.aspx