Use or write a server which records the User-Agent http field. Most of them
just ignore it, although some are starting to record it. Ones I know of are:
Apache: http://www.apache.org/ (suggested)
NCSA: (forgot, havn't been there for a while)
I would suggest Apache, because it is basically NCSA, but better. You can
configure it's logfiles to record all sorts of spiffy information.