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The only reason you will need a RIP is if your printer is NOT a PostScript printer. The RIP software will enable you to print halftones, angles, etc. to any printer Like an epson ink jet, Thermal Imagesetter etc.
Some laser printers are PS and some are not.

 

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Here is some more info. http://desktoppub.about.com/cs/rip/a/rip.htm