\newlength{\howlong}
\newcommand{\strikeout}[1]{
 \settowidth{\howlong}{#1}%
 #1\unitlength0.5ex%
 \begin{picture}(0,0)\thicklines
 \put(0,1.4){\line(-1,0){\howlong\divide\unitlength}}
 \end{picture}%
}

With this in your preamble, you can use the 
command \strikeout{some text}, and it will 
print the words "some text" crossed out.
I think this only works for a phrase that
appears on one line of the page; it messes
up if you go past a line break.