I don't know of any software you could pick up that would allow you to do this. But there are plenty of mac users here (including myself) who would be willing to help you out with screenshots and tech feedback (I run 10.2.3, with Netscape 7.01 and IE 5.2.2 currently).
Some issues to be aware of: if you are builidng an admin panel, you need to be wary of the current lacking state in which the newest Java plugin is available for mac's. I believe we are only at 1.3.1 (?) but there are some commercial text box editors that require a newer version. IE is also famous for truncating file upload paths so that the full path is not sent back to the database and your app throws an error. NS and Mozilla do not do this.
Generally what works on a PC will work on a Mac, if you write clean code and stay away from any hokey Windows/IE-only scripts.