Congratulations on getting a Macintosh computer BB. You've made the right choice. I know it was expensive but trust me it's worth every penny. Take good care of that machine. Just because it's a Mac doesn't mean it's impervious to malicious software and hacker attacks.
These are the software programs that I use and recommend.
Split and join files: Split & Concat
Unzip files: The Unarchiver (will also combine split files)
Create multiple screen captures in different time sequences: Skreenics
Editing .avi files: Explicit
Unfortunately, this software does not recognize .wmv files. I have yet to find a free software for Macs that can edit WMV movies.
Virus scanner and hard drive scanner: ClamXav and OnyX.
Audio editing: Audacity
All programs I have listed are freeware.
I'm sure you'll be doing more research and playing as soon as you get your computer. Have fun.