Radio Shack carries the computer interface cables for the PRO-96. Their current offering is a USB Converter cable. However some stores may still have the RS232 serial cable at a substantial discount, as it has been discontinued.
PRO96COM software might be what you're looking for, and it's free!
The interface is already part of the PRO96/2096, all you need is the programing cable and PRO96COM program the radio and program work with any P25 system. The program is available here: http://groups.yahoo.com/group/PRO96COM/