Ok, you can add the select list (Insert->Form->List/Menu) using Dreamweaver. After adding the list, you would want to click on it and in the properties panel click on the List Values button and add the values you want. If you're populating the values from a database, click on the dynamic button below the List Values button.
When you're done with this, you will have a working dropdown list. You will then want to add validation to the element. Go to Insert->WebAssist->Validation Toolkit. There you'll have a choice of client validation or server validation. The client validation will be run on the client's end, so it doesn't have to go through the server. The server validation will be code running through your server. This validation will be applied to the page that you are posting the form to. In this case, I would recommend just going with client validation. After clicking on the client validation, the Wizard will pop up. Select the correct form and hit next. Enter the error messages you want and hit next. On this step, you will be adding the validations. You will want to select the form element from the dropdown list. Then select the validation type you want and hit the plus button. When you're done, hit finish and the form field will be validated.
