If you are going to use Word-press to build your web site, I`m assuming that you will be hosting it on a web server, unless you have your own server at home. Since you`re going to be using word-press and WordPress is installed on the web server since you need a database and php. You don`t have to worry about whether you can run it on a mac or PC since you will be working via the web browser instead of your local machine.
Now if you were a developer / Designer, then you would need different tools such as Dreamweaver CS3 for MAC, and a Local Host in oder for you to develop on a Mac.
I hope this helps and that it was clear enough.
Web Developer / Owner / Consultant
When starting your own business the need to "know-how" is greater than money!