Brochure

I just called Kinkos and asked them what DPI they recommended for a color brochure and they said between 1300-1500. So I did this in photoshop and the lag is incredible, my usually quick pentium 4 looks really slow. What would be the best way to do this? My brochure is going to be 8.5x11 inches. Would it be better to split it into sections? Or should I just keep going along at this slow pace?