Try the following article on creating custom controls: -
LabVIEW Custom Controls, Indicators, and Type Definitionshttp://zone.ni.com/devzone/conceptd.nsf/webmain/A9FBCAA7A3D7922186256A3000652B56?OpenDocument
You might also like to look at the follwing locations (in no particular order) from Google
http://hamiltondesign-consulting.com/Cus_ctrl.html
http://members.lycos.co.uk/sgctek