I found a way with the server side object model to query a SP list:
sender, EventArgs e)
(var web = site.OpenWeb())
var list = web.Lists[
RadAutoCompleteBox1.DataSource = list.Items.GetDataTable();
My next question however is, how do I set the AutocompleteBox to search on multiple columns in this datasource? I need to generate a "hit" on several columns in the datasource.