If you are brand new to WP, I'd suggest starting with a free theme from the repository on this site - http://wordpress.org/themes/
That way, you will get a better idea of what you want in a theme before you spend money. Also, commercial themes aren't necessarily "better" and many are more complicated to use. For sure, make sure any commercial theme is well-supported - as these forums don't support them.
Suffusion is a theme with TONS of built-in options and great support from the developer, so you might check that one out.