Drawing programs like Illustrator and CorelDraw render vector artwork differently from the way they render text, and type always appears heavier when converted to outlines (in my experience). Either choose a lighter weight of the typeface, or add a white stroke to your converted outlines.

This bolding is deceptive: it occurs on screen, but will not be apparent in print.

Dear Mr. Shinn that's what a friend of mine told me, but apparently letters get bold even when printed. :(

Maybe it's the printer?

Are you converting a TrueType font to outlines? I have had some (understandably) bad experiences converting the curves in TrueType fonts to Postscript outlines in Illustrator. You can always try putting the type in one color on one layer, the outlines on a higher layer in a different color, and then adjust the outlines to match the type.

Thank you for the info James.

I'm working with OpenType Myriad Regular.

You should check if Illustrator adds a line thickness to your outline, instead of just filling the outline.

Dear Bert, how to i check it? Thank you.

The STROKE window (pallette) will show whether you have a stroke with thickness or not. Alternatively you can change the colour of the stroke to ‘none’ in the COLOUR pallette (that's the option in the lower left corner — a box with a red diagonal stroke in it).

For whatever reason some laser printers add weight to outlined body text. The only solution is to not convert to outlines or to compensate with a graded version of the font or add a hack white hairline stroke.