HTML/XHTML - because Wordpress uses XHTML. Hopefully they will teach you the latest standards and good coding practices.
HTML 4.01 Specification (which forms part of XHTML)
XHTML™ 1.0 XHTML™ 1.1
Dreamweaver it a tool. It doesn't matter what tool you use, you need to know HTML/XHTML to problem solve when working on your blog/site.
Full Photoshop has a large learning curve but there are lots of tutorials around to help you learn that.
Adobe bought Dreamweaver (in case you didn't know that). The Adobe packages are quite expensive to buy. If you are serious about how to code and design your blog/website it might be worth it to buy. There are other programs available with a smaller price tag if you didn't intend on getting really serious or your budget is tight.