My (now sold) empeg currently has 2 x 18Gb hard drives in it. It's new owner has asked me to upgrade one of the drives to a 120Gb drive that he has provided me with.

Does it matter if this bigger drive becomes the primary or secondary drive? I'm not fussed about losing what is on the existing drives as they will be wiped anyway - what is the best (and/or easiest) configuration?