I'm not a real JavaScript expert either, but as was mentioned JavaScript is not Java, and it should be platform independant.
That said, here are somethings to watchout for.
1) JavaScript might not be able to be interpreted by all browsers when writing web apps. (ie. Lynx or other text based browsers). That is it's one limitation since it's interpreted, is how the browser interprets, and processes the commands.
2) There might be some books out there geared towards windows JavaScript implementation using WSH (Windows Script Host). This is that little engine that Micro$oft invented to make Network/Desktop Admin's jobs easier through automation... it can process JavaScript or VBScript, even PERL and TCL if you add the plugins. WSH is nice for windows, but this is the same pandora's box that causes a lot of the vulnerabilities with Worms. Since this a Mac forum, I'll end my WSH talk there.
3) JavaScript can be used on the Mac with a program called Konfabulator. I'm a Mac newbie myself, and haven't had much experience with Konfabulator, but from what I understand you can write your own widgits using JavaScript and XML, and Konfabulator will act as the interpreter. I'm sure more information can be found on this on this site or by doing a google on Konfabulator.
All that being said, I recomend O'Reilly's JavaScript the Definative Guide, and I recommend going out to a site like hotscripts.com or webmonkey.com, getting some good sample scripts and ideas, tweaking them, playing and learning.
See ya,
Myron