@misty Are you interfacing with something that requires more of the RS232 standard than the typical DB9 connector carries?
I've never encountered stuff that wouldn't work with the signals on a DB9 RS-232. If you have something like that, I'd be surprised if it worked with a USB adapter at all.
And if it doesn't need the DB25, DB9 + adapter (or correctly-ended cable) should be fine.
You def. want an adapter based on the FTDI USB-RS232 IC. The others are inferior.