Define your own command where the labelname, the one printed by biblatex on \citeauthor, becomes given-family, that is, the first and the last name.
\newrobustcmd*{\citefirstlastauthor}{\AtNextCite{\DeclareNameAlias{labelname}{given-family}}\citeauthor}
Example:

The main.tex file
\documentclass{article}
\usepackage[natbib=true,sortcites=no]{biblatex}
%\citeauthor prints only the last name. This command prints first and last name.
\newrobustcmd*{\citefirstlastauthor}{\AtNextCite{\DeclareNameAlias{labelname}{given-family}}\citeauthor}
\addbibresource{library.bib}
\begin{document}
This is a citation from \citefirstlastauthor{knuth2001things}:
``The assumption that the Bible is God's word is an unprovable axiom%
that I tend to find confirmed as I look at it.'' \citeauthor[p. 191]{knuth2001things}
\printbibliography
\end{document}
The library.bib file
@book{knuth2001things,
title={Things a computer scientist rarely talks about},
author={Knuth, Donald Ervin},
year={2001},
publisher={Csli Publications Stanford, CA}
}
biblatexis an option, perhaps this post will help you: http://tex.stackexchange.com/questions/24979/citing-authors-full-name-in-biblatex – hpesoj626 Dec 08 '12 at 10:38