The versions of web developer-like plugins for Safari, just suck; it's as simple as that. Otherwise I'd be on Safari. But it's far more proprietary-behaving than Firefox.
2.) Download Drosera. The download instructions for Safari 3.1/3.0 have you download a version of WebKit, but you don't need to install it. Just install the version of Drosera that comes in the DMG. You'll also need to enter the command to enable WebKit script debugging (provided in the link), restart Safari and you're ready to go.
I think FireBug still beats the Web Inspector/Drosera combo in a few areas (e.g. I'm not sure if you can dynamically alter CSS like you can in FireBug) but these tools get you most of what you're accustomed to in FireBug.