The type of computer and operating system you have doesn't matter for snitz. Once your files are uploaded to your website you can use any computer to begin to set it up. It is all web based.
If you want to edit any of the snitz asp files, you can open them in any text editor such as textedit for mac.
You likely won't be able to host a web server using Snitz on your Mac, though. Even if it was possible, and I'm not sure it would, you'd need to buy Sun One ASP.
If you're uploading it to a webhost I don't think it matters does it? I use three different computers to manage my forum. I have a Mac with Leopard, a PC with Vista and a laptop with XP. I can even use my older computer that still has Windows 98.