just learn the basics of dreamweaver, perhaps learn wordpress for blogs and learn PHP, HTML & CSS ..also a web designer is expected to have graphics art skilss these days, well i think graphic artists are expected to know a bit of html as well ..
it's always going to be a regular form of employment that is always in demand.
just remember that a web designer has to spend alot of time talking with clients on the phone and interacting with other departments so it's not really a job where you can stay secluded and it can be challenging.
i would only recommend this line of work to someone who is a genuine optimist as annoying as that sounds you are going to encounter alot of frustration and errors, failures, and a strong memory and grasping concepts is a huge advantage.
also remember that you have to continuously upgrade your skills each year. so it can be quite complicated
as was stated above studying multimedia or website design will be superseeded withing a year or two so any certificate while still valid won't be rooted in terms of relevance if companies start using a CMS or new ways to build sites that become industry standard techniques because languages are always changing and methods such as programming is being made simpler each year so that soon anyone will be able to download software where they can add images to headers and footers and can just add content theselves, that's why Joomla and CMS's are the norm right now.
i think right now web companies tend to focus on building the template for Joomla CMS's and JQuery is popular because they make advertisements and moving artwork and vidoe look so slick.
you really have to be 100% interested in design and programming otherwise you will be lost along the way.
its fun to try as a hobby though and you can go at your own pace.