Here's a few links which might help you out:
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3ED5D56A4E034080020E74861&p_node=DZ52049&p_source=External
http://zone.ni.com/devzone/conceptd.nsf/webmain/F9C57D78E202C1F286256802007B8C00?opendocument
http://zone.ni.com/devzone/conceptd.nsf/webmain/A4F70983EEB8762B86256802007B8BFD?opendocument
http://zone.ni.com/devzone/conceptd.nsf/webmain/8519EB50E14EBC5C86256802007B8C02?opendocument
There are also some DDE examples in the \CVI70\samples\dde direcory.
Regards,
Ryan K.