You have to be a member to download code but all that is required is an email address and password.
Once you have installed it, while in the IDE, click on Tools, Add/Remove ToolBox items and then browse to the dll file and select it. The control will show up on the components area and can be drug onto a form design surface like any other combobox, textbox, etc.
Here are a couple gotchas I encountered:
1) If you are going to define SourceDataTable in code then set the Loading property to ComboboxItems at design time and then change it in your code when you set the SourceDataTable property.
2) You can use the standard combobox DataSource property for Tables and then you can use ValueMember and DisplayMember as you normally would. HOWEVER, if you are defining them in code, you MUST set up the SourceDataTable property first and THEN the DataSource, otherwise you will get an error.
3). It does not currently support filtering by using a DataView with a RowFilter. It will work, but the drop down portion will not draw properly.