Products from Apple with "i" in front of its name (iMac, iPod etc.) are written with a lower case "i" followed by an uppercase letter after that. Spelling it with an uppercase "I" (e.g. Imac, Ipod) is not recommended.

Similarly, Mac OS "X" is pronounced as "Mac OS TEN", not "Mac OS Ex". The "X" denotes the roman numeral ten. This is also reflected in the Text-to-Speech on your Mac if you set it to read a sentence with the name "Mac OS X" in it. It'll pronounce it "Mac Oh Es TEN".

..similarly, "OS" isn't pronounced as "ohs", if you do not know that already.

Mac is spelled as it is: Mac. Not MAC. That would be "Media Access Control". The range of computers made by Apple is called 'Mac'. It used to be called 'Macintosh', but the recent product lineup names have all been simplified to just 'Mac'. Most Mac users prefer to refer their machines as "My Mac" rather than "My Apple".