Mike Pope has a great blog post tonight that walks through a common scenario I've seen asked a lot on http://forums.asp.net lately. Specifically his post covers how to embed a DropDownList control -- whose ListItem values are databound against one database table -- within a FormView or GridView control, and have the SelectedValue of the DropDownlist be two-way databound against the results from a separate database table.
For example: you could have a FormView control that shows an individual product's details from Northwind, and have an edit view of that Product that allows you to change its category value. Rather than expose the category as the raw CategoryId number, you want to have the categories be surfaced as a friendly drop-downlist of category names (with each item value being the appropriate categoryid).
Mike shows how to-do this with ASP.NET 2.0 and no code using the new <asp:formview> control, and two-way <%# Bind("columnname") %> databinding syntax. His sample uses the new <asp:accessdatasource> control for the databinding, but you could use the exact same technique using the Northwinds DAL I built a few weeks ago and the <asp:objectdatasource>
Hope this helps,