If this has been covered elsewhere, please direct me!

I know how to access a DataContext for my own databases, but not those internal to DotNetNuke.
I am trying to give an admin the capability of selecting a name from a dropdown of all users, in order to assign them to a specific task.
I tried searching for User Lists, but can only find something for specific roles, and do not want to limit an admin that way (except to exclude the Host, I guess).

<asp:DropDownList ID="ddlUsers" runat="server" DataTextField="???" DataValueField="???" />
...
var colUsers = from Users in ???
               select Users;
ddlUsers.DataSource = colUsers;
ddlUsers.DataBind();

I am using DNN 5, VS'10, and C#.  Thanks

Sorry I forgot to thank you for the reply.  This may have worked; soon after this my pc failed and I had to upgrade to Win 7.  If I can ever get DNN reinstalled, I'll try this code again.  Thanks