Printers usually can't print right to the edge of the paper. Imagine how fast the shiny metal surfaces would get gunked up and jammed if ink/toner was squirted on them because droplets missed the edge of the paper.

To get full bleed colour (whilst keeping your printer in working order), the basic method is to print as close to the edge as you can and then chop off the edges with scissors or guillotine. If you want your final piece of paper to be a specific size, you have to print onto a larger piece of paper and then cut it down to that size.

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Andrew Lockton
Chrysalis Design, Melbourne Australia