Glad to hear you got your modem working. I thought you had given up.
I'm not sure what graphical tool is included with Mandrake for doing this. There is one in Red Hat as well, but I don't use it. I prefer to do most of this stuff from a command line. I also assume you mean a utility to start and stop services, rather than configure the individual services. To set enable/disable services I use the "chkconfig" command. To start/stop the services I use the "service" command.
e.g.
$ su -
(enter root's password)
# chkconfig --list | more
will list all of your services and tell you if they are on or off for each run level. For instance, on Red Hat Apache is listed as "httpd" so to enable it so it starts at boot time you would:
# chkconfig httpd on
And to start it immediately you would:
# service httpd start
For more info on the chkconfig command you can type "man chkconfig".
Again Red Hat comes with graphical utilities to configure many of the services but I prefer to edit the config files directly in an editor (I use VIM). For instance to configure Apache I would edit the "/etc/httpd/conf/httpd.conf" file which is the main Apache configuration file.
Another great utility for configuring your services is a web based utility called "webmin". I am not sure if Mandrake comes with it or not, if not you can get it from:
http://www.webmin.com/An advantage of webmin is it runs on most Linux distros as well as other popular UNIX systems so if you know how to use webmin to configure one OS you can configure any of them. Personally I like webmin for configuring PostreSQL and my firewall rules because webmin makes these two things pretty easy.
I know that is a side step from the question you asked but I thought it might be helpful. Hopefully someone here more familiar with Mandrake can answer your exact question.