You must be using a fairly recent v2.4 kernel for this. You may wish to read over the whole section before proceeding.
Hotplug will allow you to automatically run your syncronization software when you press your sync button. You will only be able to configure this to sync for one Visor. If you need to be able to sync multiple users with differen Visors, you can't. (With different Palm's and Clie's, is a separate question, to which I don't know the answer to).
You will need to enable "Support for hot-pluggable devices" under "General Options" in the kernel config. This is the kernel option CONFIG_HOTPLUG. Make sure you compile/re-install.
You need to get the hotplug scripts from the linux-hotplug homepage: http://linux-hotplug.sourceforge.net. The scripts are available as a rpm package or tarball If installing the tarball package, please read the README file that is included on proper installation procedures. If all you are configuring is the Visor hotplug support, then most likely you'll just have to do this:
gzip -dc hotplug-2002_08_26.tar.gz | tar xvf - cp hotplug-2002_08_26/sbin/hotplug /sbin/hotplug cp -r hotplug-2002_08_26/etc/hotplug /etc
When all is said and done, an (executable) script named /etc/hotplug/usb/visor should get run when you press the hotsync button.
#!/bin/sh /bin/su rvbijl -c /usr/local/bin/coldsync
Obviously, you would want to replace the rvbijl39 with your normal user account. And make that script executable.