Waht to do with a down loaded disc image file

I'm new to Mac and stumped here.

I've downloaded a program file which arrived as a .sit file.

It unstuffed to one folder containing a .txt serial number file, and another with a .toast extension which is 89.6 megs.

I can get the serial number, but can't seem to do anything with the other.

The problem is my inexperience with Mac and how these things operate.

Please help by walking me through this.

Thanks

Rick

Roxio's Toast disc burning and creation software http://www.roxio.com/en/index.jhtml is needed to open .toast disk images