Hmm well without reading the job description it may be tough to give you advice.
If the listing is for a job and sometimes you MIGHT be updating an existing site, etc. Knowing how to get around Dreamweaver may get you by.
But, if the job is for a web position where you will be building sites from scratch or making big changes to existing sites then a listing that says the candidate must "know Dreamweaver" is a red flag -- because you don't need ANY program like that to build a site. They should be asking for someone with strong HTML/CSS skills, PHP, etc.
The point is this... if all you can do in Dreamweaver is click on something and change it within the constraints of the system, what are you going to do when they ask for something that Dreamweaver can't do?
Also, browser compatibility -- you need to be a code monkey to troubleshoot what the site will look like in:
IE 6, IE 7, IE8, IE9 (soon), FF, Safari/Chrome
Often you will need separate CSS files to handle multiple browsers. Dreamweaver will not be able to do that for you.