WordPress and Apple

Hello all. I need some help. ?? I purchased a website a few days ago and started a wordpress blog throught Yahoo. I would like to gain more variety in my themes and tried to upload one that I downloaded but I am unsure of how to do so.\

I also would like to learn how to design my own wordpress themes and am in the process of learning HTML.

I run an Ibook G4 on a PowerPc. I have the entire adobe suite including Adobe Golive. Since I am a begininer, someone suggested I work on it through Apple’s textedit first.

But I would appreciate any help you give me. I am sorry if I appear green but I really did try to read through the entire wordpress site before I asked.