Not with "just" software.
The USB and Rs-232 protocols are different enough to require an interface converter.
The good news is that Black Box does offer 1.
"USB Director RS-232 (Single-Port)
Here?s a handy way to turn your USB port into a high-speed serial port."
The bad news is that the way their web page is structured, I cannot provide a direct link.
http://www.blackbox.com/
From the main page, select products and follow along from there.
I am sure that there are other sources that would sell an interface converter for less.
Chas