Well, now I don't feel such an idiot. Just found this on BookBrewer's website:

Unfortunately, centering text is currently not supported in eBooks. Spacing the text over is not recommended, as what looks centered in one eReader device (like an iPad, Kindle, Cruz, etc) may not look centered in the next eReader. This is because each eReader has a different sized screen, and so one may have more characters displayed from left to right than the next.

Sorry for the bother, folks! Thanks all the same,

kat