paxx - very true, except that the details of the file type are kept in an area called a resource fork, and the file itself is kept in the data fork. Also, most Macs have a little tool called PC Exchange installed which looks for PC file extensions and will set the creator and filetype IDs to predetermined settings suitable for a Mac application to then recognise.
Graphics Converter is a great tool too as it'll open just about any file you throw at it regardless of the Creator/type settings in the resource fork.
I forget what it's called, but there is a tool too which lets you see additional info on files when you look at the file Info, including the raw 4 characters for creator and file type, and will let you set them by hand...or, you can go to PC Exchange and tell it about additional file extentions to convert.
....and they say Macs are easier?
They are when they work, but just like PCs, once you need to get stuck into the detail, it can all get very complicated for people not used to this stuff.
