you can also download rybka 2.2 to analyse games with SCID. it's the best engine other than rybka 3 (which makes it better than fritz), and it's free. check out www.rybkachess.com.
if you insist about fritz though, you should visit www.chessbase.com.
If you need multi-line analysis, go download SCID at http://scid.sourceforge.net/
It is a FREE open-source mimic of chessbase with 3 powerful engines to pick from to do your analysis.
HTH,
Shiv