Im sorry, but you're a bit lost here.
I dont even know where to start.
Pantone is a color-system independent of others. Basically the CMYK values you get from the pantone-chart isn't even going to match up to the particular pantone color in print.
I'm just going to write down some points for you to consider and to research upon before doing anything else.
* Is the pantone chart older than 6months, or has it been exposed to sunlight?
* Is the color and CMYK conversion numbers you are checking against for coated or uncoated paper?
* What kind of print will the endproduct be? Offset-printing, digital printing?
* What kind of icc-profile does your printer use?
* Did you calibrate your screen with a photo-spectrometer? If so against what Kelvin? 6500? 5000?
* Did you calibrate your screen within the last 2 weeks?
* Have you set up your system and workflow to use the correct color settings?
* Do you have photoshop/illustrator set to preview proof colors?
* What kind of ambient lighting do you have in the room? Do you use a hood for your screen?
I could go on, if you are unsure about any of the points above, no the color wont match, and it has nothing to do with your particular imac (although one could argue that a matte screen does give a more color accurate preview for print).
Just use the correct values (in cmyk or preferably the pantone-color in the illustrator color palette in your CS application) and use the pantone book as a reference (thats whats its for). Make sure your color settings and ICC profiles match and recalibrate your screen against 5000 kelvin (which is the temperature the sun gives off) for print work.
Good luck.