A good start would be Runway or CWS - they both have simple forms you can dissect to get your head around it.  Personally, I'd avoid AJAX for the core functionality of this, and would only use it to enhance a server-side solution ('progressive enhancement').

Hope this helps...

Dan, thank you. I installed the Runway contact form package, it seems like it's functionality is based on sending emails rather than data collection? Am I understanding correctly?

Hey Amir

You need to get a subscription o Umbraco.tv

http://www.umbraco.tv

and watch this video

http://www.umbraco.tv/documentation/videos/for-developers/working-with-data/creating-data-programmatically

It covers everything you are trying to do...

You can propably glean something from this:

MemberGroup mbg = MemberGroup.GetByName(ctrlDropDownListPosition.SelectedItem.Text);
MemberType mbt = MemberType.GetByAlias("Extranet member type");
Member m = Member.MakeNew(ctrlTextBoxEmail.Text, mbt, User.getAllByLoginName("admin")[0]);

m.Text = m.LoginName = m.Email = ctrlTextBoxEmail.Text;
m.Password = ctrlTextBoxPassword.Text;
m.getProperty("name").Value = ctrlTextBoxName.Text;
m.AddGroup(mbg.Id);
m.Save();

You must use a your usercontrol

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