Just my 2 cents......
If you want to get into professional video editing make sure that you have a dedicated computer that is built for that purpose.
Now on the Windows platform....AVID is probably the most known system. Various levels of pricing. Also Adobe Premier, Vegas, InSync Speed Razor are also very good packages.
On the Apple MAC Platform you have AVID, Media 100, and Final Cut Pro.
At my office we have the AVID and Final Cut Pro on MACS. I've been using both systems now for two solid years and I'm still learning new stuff.
Both platforms have pros and cons. Until 2001 I had never played with a MAC. Since using the two that we have I can say there are things I like and don't like. Besides money! The biggest choice is simply you deciding what software interface works best for you.
If you have any specific questions I'll be glad to address.
Joe