Debugging javascript in Safari for Windows
Well, apart from the Error Console that can be opened from the Develop menu (which in turn can be enabled in (Prefences / Advanced / Show Develop menu in menu bar) there aren't many javascript debugging options in Safari AFAIK.
Still, the error console is quite useful as it shows javascript errors and also lets you to execute arbitrary Javascript statements.
Since you are on Windows anyway, you could try using the inbuilt Javascript debugger of Google Chrome, which is a browser very similar to Safari (although the Javascript engine is different).
I stumbled across this question via google - although it's rather old, none of the answers are quite right, (due to safari being updated to 5.1 since this question was asked)
Enable the develop menu as DrJokepu mentioned:
Prefences / Advanced / Show Develop menu in menu bar
Now you'll see an option in the page menu to Show Web Inspector, which gives you very similar tools to those found in chrome, (Details here). You can also start debugging javascript directly from the develop menu.