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I would learn usability concepts, the study of how users interact with websites. Jakob Nielsen has a couple books on that that are worth reading.
I personally wouldn't worry about spending time with java. Learning some Internet Marketing will greatly enhance your web design skills, IMO.
As far as server-side languages are concerned, you may want to learn both ASP and PHP. Personally, I don't care for ASP, but MANY potential employers do.
You should probably get a basic understanding of PHP and ASP, just to have your bases covered(albeit, only two bases).
As a developer you need to start with what the site is suppose to do and then deside how best to impliment it. In theory, a developer is mostly a project manager: deside what need to be done and who to do it. In practise, deside what needs to be done, do what parts of the job forwhich your skills are suited, and if necessary, farm out the rest.
In my experiance, programing tends to lend itself better to development than does design, but there are plenty of designers who are able to also see the big picture. The saying "Don't judge a book by its cover," applies to Websites even more so, but it can be hard to remember when you're the one who desinged the jacket.