Let's say you want to download and use some custom control available elsewhere on the Web. How do you add it to the Web developer so it appears on the toolbox and is picked up by intellisense? Here is how:

1. Download control assembly. I used BusyBox as a test control.
2. Unzip control to a folder of your choice.
3. Open Web site in the Visual Web Developer or Visual Studio 2005.
4. Right click on the Web site node in the Solution Explorer and choose New Folder.
5. Create bin folder. It should change icon to the special icon, different from a regular folder.
6. Right-click on the bin folder node and select "Add Existing Item...".
7. Locate control assembly, select it and click OK.
8. In the Solution Explorer right click on the bin node and choose "Refresh. The control assembly should appear under the bin node.
9. Select the desired tab on the toolbox, right click on it and select "Choose Items...".
10. Click Browse..., locate control assembly in the bin and click OK.

Controls in the assembly should now be visible on the toolbox. You can now drag them onto Source or Design view and see intellisense for control tag and its attributes.