iMac 21.5...which one?

Well, the one with more memory might be better, but don't forget that Apple sells "refurbished" iMacs very cheaply on their official website (see link, below), so you could possibly save so much money there that you could get an even BETTER one!

If you're not familiar with "refurbished" computers, they are machines that have been returned for one reason or another and are then gone over with a fine-tooth comb by a technician to make them perfect and then re-sold at a HUGE discount and they still have ALL the original warranties on them, too! My own iMac is a re-furb and it has been working flawlessly for years, so go for it, you could save big!

Good luck!... :-D

the graphics card processes the computers display output, so it renders 2d images and 3d graphics.

that means unless you play video games or use advanced editing software (not imovie) then you will be fine with the cheaper one(the HD 4670) .even the lowest ones have far more power than needed to accomplish the tasks you listed and if you spent the money on the better one i doubt you would see much difference while doing those things. but if you do want your computer to be faster then get one with a stronger processor.But like I said, they make them pretty fast as it is these days so you should still be fine. good luck with your decision.

No pc, which includes the iMac, comes with MS workplace. some have trial variations, yet none incorporate the full version. you ought to use Libre workplace, Open workplace or Neo workplace, all loose, or purchase MS workplace 2011 for Mac or purchase iWork.

rule of thumb - if its dearer its better