Word is a pretty poor tool to use for web pages, especially where forms are concerned. You can indeed use an Access database to populate a drop down list but this is complex at the best of times and would also require ASP language and Microsoft Access database support from your web host.
If you have an alternative editor available for creatng your web pages I suggest that you use it. If not, you may have to bite the bullet and dig into the source code.
Here are a couple of links to online tools that generate the necessary code to make a drop down listbox:
The excellent (and free) HTML Kit is a web page code editor. On the Forms tab it has many form features that you can click on to jump start your coding. One of these is a listbox tool, so you may want to download and try it:
Another very good web editor to consider is the free ASP.NET Web Matrix from click here
It was originally released as a.NET code editor but it has some FrontPage-like features that allow you to drop form elements onto HTML pages and edit their values to suit. It's only a 1.3mb download and is one of the best little developer tools I've played with for ages, but it does still require that you know how to code the form element, so you may find that it just isn't worth the bother.
The form tools in Word are meant more for programmers who want to integrate Word documents with Access, Excel or whatever and are mostly used in conjunction with Visual Basic or Visual Basic for Applications code. Using them for the web is possible but far more difficult than the effort required to get your head around it, in my opinion.
A month or two ago PC Advisor carried various web authoring programs on its covermount disks, and you would certainly find form editing tools for listbozes and option selections in them.