Don't forget to load fontenc with the T1 option; \DJ and \dj are not available in the default OT1 encoding. Add in your preamble:
\usepackage[T1]{fontenc}
Here's a little example, producing your letters:
\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage{currvita}
\begin{document}
\v{s}\v{S}\DJ\dj\v{c}\v{C}\'c\'C\v{z}\v{Z}
\end{document}

Loading inputenc with the option utf8 (if your editor supports unicode), you'll be able to write some (and possibly all) of those letters, directly from the keyboard:
\documentclass{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{currvita}
\begin{document}
ćĆ
\end{document}
I don't know if this is possible for the remaining letters since I am not familiar with a "Croatian keyboard".