Hi there, Ive been in the digital prepress for a while, and IMHO you dont need resolutions as high as 600 ppi for most of the regular printing needs. In Mexico the common numbers are 150 lpi (lines per inch) for a magazine, so we use 266 to 300 ppi (pixels per inch) or dpi (dots per inch) for the artwork. Using a dpi resolution above this will only take more time and effort for the RIP (Raster Image Processor) to process your file. Just make sure youre working in CMYK mode (if you need a color output) or grayscale (just plain black&white) in a format without compression. TIFF is the most supported format and the easiest to rasterize. EPS is used when you need clipping paths or special spot colors, but only useful with a PostScript printer or imagesetter. Hope this helps... and yes, ask your printer. :)