This page shows how you can implement cascading dropdowns on a SharePoint new
item form. The Web Part on the left side of this page is the same
List Form Web Part (LFWP) you would see on NewForm.aspx for the Sales
Opportunities list.
This page uses the
SPCascadeDropdowns function of the
jQuery Library for SharePoint Web Services.
Because this demo uses Web Services, anonymous access will not work.
When you are prompted for credentials, use these:
Username:
demouser
Password: demouser
(As in "Demo User" -- nothing to do with rodents.)
You can download the jQuery for this demo
here.