Yes there are drivers, they should work for macppc as well.

See http://netbsd.gw.com/cgi-bin/man-cgi?ucom++NetBSD-current
and
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/i386/conf/GENERIC?rev=1.714&content-type=text/x-cvsweb-markup

and just copy and paste the lines similar to:

umct*	at uhub? port ?		# MCT USB-RS232 serial adapter
ucom*	at umct? portno ?


Quoting dixie <dixieml@imap.cc>:

> Hi list, before buying one I'd like to know if USB to RS232 adapter are
> supported by NetBSD/macppc :)
> Is there any known problem in using such kind of devices?
> Do they really need a driver? (in GENERIC conf file I did not see
> anything related)
> They usually came with a drivers' cd for Windows.
>
> Thank you.
>
> --
> 	dixie
>
> I'm here only to improve my Inglisc.