--- You wrote:
Does anybody know of an echo canceller for a desktop PC
that hasn't been cancelled?  The Polycom and Clearone solutions
have been, 
--- end of quote ---

polycom equip is still available, for example, from CDW, below.
the interconnect box is required and works with several of the soundstation
models, like the least expensive one below.

http://www.cdwg.com/shop/search/results.asp?key=video+interconnect
http://www.cdwg.com/shop/products/default.asp?EDC=092253

-gurcharan
===========================
Gurcharan S. Khanna
Associate Director
Research Computing
Dartmouth College
gkhanna@dartmouth.edu
office: 603-646-1644
http://research.dartmouth.edu/
http://www.dartmouth.edu/~gkhanna