Further to my post which included details of NovaMind— if you're looking for some Mind Mapping software and don't want to spend any money, you should investigate FreeMind. It's available for Windows, Mac OS X, Linux,… in fact any OS with a JVM (because it's a Java app). It works great, but it has fewer features than NovaMind.
One of the nice things about Open Source software is the developers by and large aren't bothered that users might somehow find out about a competing product and switch to it. In fact they are usually quite open about other products already available. If you take a look at the FreeMind Wiki pages you'll find an entry for Alternatives to using FreeMind, which lists some other free and commercial Mind Mapping programs. I see that sort of thing quite often on FOSS sites, and it always makes me smile. You just don't normally see information like that on commercial software sites.