Do i have to create files in 300dpi when they should go to the printers? My computer is having a little trouble loading the huge amount of data laying in the rams when i change something in the file (I Use Photoshop CS3)

I always use 300dpi. The more information you give the better off you'll be. Remember, the printer can't add density. And if he has to enlarge your design, you will be in trouble with anything less. But someone might disagree with me. That's just my experience.

It is better to use 300dpi for printing.Although in some cases it slows the computer it is really a reliable one.

300dpi or nothing. I used to send images at 74, but they were so grainy! Now I have clarity, and crystal-clear lines on all my images, which really makes a difference in the first impression and the opinion of my customer when it comes to what they think of my business.

I suppose it depends on the print format for example: Newsprint 150-200 dpi & Magazine 300 dpi.