There are tons of math fonts available. The "Symbol" font that ships with windows has a bunch of math symbols in it. if you need more, there are tons available online.
E.g., you can get the Mathematica fonts from
here for Windows or
here for Mac, for free. There are tons more available, including
ComputerModern from LaTeX.
What word processor are you using? OpenOffice is free, compatible with MS Word file format, and open source, and even has its own Math equations editor.
http://www.openoffice.org/
And if that's not powerful enough for you, then just download LaTeX -- there are many free distributions, and leave non-math-friendly Word Processors behind you for good. (I have.) Here's a good place to get started:
http://www.ctan.org/what_is_tex.html
It has packages for pretty much everything, and I'm sure it can do everything ChiWriter can do... and a whole lot more! (In fact, here's
A ChiWriter to TeX converter (among other things)--and if you really want to go back to using ChiWriter, it looks like you can
get a tool for making it make PDFs here... though the output shown there is extremely ugly compared to
the beautiful things LaTeX can do, IMHO...)