How do I create a Theme (Skin and Stylesheet)?

I'm using Visual Web Developer Express 2008 with an ASP.NET 3.5 website.

I take it the only way to create a CSS and skin is by manually typing these
in line by line in the page editor? There is no automated process?

My goal is to emulate a look and feel similar to www.communityserver.com. I
haven't had any formal design training before but rather programming only so
I hope an end result looks OK.

Is there also any guidance anywhere about recommended aesthetic do's and
don'ts when creating style sheets and skins?

TIA