Blowing up pictures - min. resolution.

[black_2.5RS]

I'm thinking of printing out some larger images (50x70cm). Is there a minimum resolution / megapixels or size I need to have in order to have the picture turn out w/out any blurring or loss in resolution? I realize some of this is dependent on the quality of the printer (but assuming that's a non-issue b/c it's going to a print shop). I took some great pictures over the last couple weeks w/ my new dSLR (Canon XSi) and thinking about getting them printed. I also hear that printing in RAW file format might be better for this? Is this correct?

[483hp]

Depends on how you are going to use it.

If you want a magazine quality image, 200ppi is the minimum, ideal would be 300ppi

If it will be used like an exhibit display, ie: viewed from a few feet, most print shops will request 150ppi, but will accept 100ppi as the practical minimum.

RAW format has no effect on the image resolution. It just gives you more flexibility to fix and adjust the image after you shot it. You still need to develop the RAW file into a jpg, TIFF, etc. in order to print it.