supposedly windows 7 is less demanding than vista, so you might see some performance gains there.
Still, upgrading windows is a dangerous game. Sometimes it works fine, other times it deletes everything. Enough that most computer professionals will tell you to run a clean install.
I did manage an upgrade from XP to vista, but your mileage may vary.
One thing I learned in computer repair - never swear at or hit a Macintosh computer. It will remember, and it WILL get you back.