If you want to just get something done quickly, you might start with a free, GNU-licensed WP theme and just change a line here or there to get the look you want. Building a WP theme from the ground up can be difficult for a new developer, so don't be afraid to under-do it at first. What you create doesn't have to b built perfectly, as long as it pays the bills.
Having said that and properly placed profit above perfection, there are others who may disagree strongly with me, but when it comes to learning something new, I say it's best to learn it from the ground up.
Learning:
[
html5doctor.com...]
[
google.com...] (not trying to be a jerk. There's a lot of good stuff out there.)
Libraries (like Blueprint):
Skip Blueprint, jQuery, etc., and just try hand-coding it by copy-pasting rules from reference sites like w3schools.com; otherwise, it will take forever to know what you're doing.
Once you learn the fundamentals, you'll be free to use whatever library you like (I never use CSS frameworks, but I almost always end up using jQuery) and you'll have an ability to adapt to changes in the technology, like all the cool new stuff in HTML5, h.264, etc.
Validation:
Install these naaoww
[
getfirebug.com...]
[
users.skynet.be...]
Lastly:
Since you're going for that OSX look on multiple platforms, I'm guessing that you're using a Mac. It's worth your while to install VMWare Fusion or Parallels and a Windows virtual machine for testing because every stinking version of Internet Explorer will render your design differently. It really is like developing twice for each browser. I'm not trying to scare you, just equip. Good luck.
