First thing you need to do is learn CSS. You can't expect to style anything if you don't know the technology used to do it. I would start with the HTML-Dog tutorials, and go from there. More importantly is actually having a good sense of design, and that is much, much harder.
Design skills don't have anything to do with dreamweaver. To develop a good sense of design, you need to start getting introspective about the sites you visit. Think about why things look good or bad. Paired with your CSS knowledge, when you see something that looks cool, think about how you would implement it. If you dont know, the source code is right there so take some time to figure it out.
I have been doing this for about 5 years or so now, and I still suck at coming up with new designs. (although, I am better at it then when I started.) What I do when I start a site is rip off the basic design from somewhere else, and make it my own. For asp I use devexpress controls, which have alot of great looking themes, so usually I just end up extending the look and feel of the controls to the rest of the site.