you should not need to restart your machine, just close the console window and open a new one.
I would also say that constantly adding everything to your global classpath variable is a very bad thing, try to avoid this. You could do what I do and create a batch file that dynamically sets your classpath for your working environment.
Or like Tualha says, add the jar to the extensions directory (though many hardened developers may frown on this too ...) better to keep development specific jars contained in their own environment, so as not to cause problems later as you need to use more and more Jars for your development.
If you want an example of a bat, let me know and I'll dig one out.