LaTex - how to create boxes with fixed heights and widths, with enclosed text that is vertically and horizontally aligned?

Suppose you want to create the box of 40pt height and 3cm width:

\vbox to 40pt {\vfil
\hbox to 3cm{Some info}%
\vfil
}

You could use whatever packages to make your flashcards, and then save the output in pdf format (use pdflatex for example). Then, make another document in Latex which uses pdfpages package and uses its nup option to print two pages per page. Pdfpages has a lot of options, to fine-tune the page layout. That gives you all the power of the other packages for your use.