To get to the printr driver, you will want to go to the printer Properties which is either accessible from Page Setup, Print.., or from your Printers panel in the system (on XP, you can either get to it from Start/Printers and faxes, or from the Control Panel).
In your properties dialog box there should be a Printing Preferences button to specify things like Paper/Quality, etc.
In that Preferences tab, there will be choices that affect the output of our print. For example, you will have a choice to Scale to fit or 100% (or other percent) of normal size. You might need to play with those or other settings to get the output you need.
Typically, though, I'm printing from Lightroom and the page layout does fine for me, resizing the image to the size dimensions I need. Maybe when you go to the Page Layout dialog and set up your job, you could do a screen shot of your final design and post it here -- we may be able to catch something.