documentclass{article}

begin{document}

setlength{fboxsep}{-fboxrule}

fbox{parbox{100pt}{Some text, some more text, and thelinewidth}}

% here I'd like something like parboxheight or similar
fbox{parbox[][100pt][t]{100pt}{Some text, some more text, and thelinewidth, and the height?}}

end{document}