I have a US Robotics external modem connected to ttys0 and it connects fine but will freeze and lockup the entire machine at random times. I used to think it was Linux, but I have now reduced it to the modem. Could there be some kind of driver issue? Another thing I have noticed is when it does freeze, the bottom of the modem is extremely hot. Ambient temp is fairly cool in room. Any Suggestions are greatly appreciated.

Did you uncheck any of the services to boot at startup with the services tool? Does the computer hang only when you start mozilla? If yes then the problem is in one of the services that boot on startup, make sure you haven't unchecked any service related to 'network' or something.

the modem will connect and sometimes stay connected for 5 minutes and other times stay connected for over an hour. It just varies. I checked the network services and all seem to be ok. I rounded up another external modem and plan to check with that tonight.

I just ran across your post. I'm having the same problem on an IBM Netvista. I've narrowed it down a bit but still haven't found the solution. Mine keeps freezing as well but only when I'm connected to the network and I am downloading http or nntp. FTP and SMTP do not seem to cause the freeze. I'm running Redhat 7.3 and is also happens when I try to run the Update Agent. Did you ever find a solution? I've checked all my logs in /var/log and can't find any messages that seem related to the freeze...I never get a core dump or anything, it just freezes. It happens in any browser or news program. IMICI also causes the freeze and it happens in both GNOME and KDE. Any guidance anyone can provide will be greatly appreciated.

Well, dont know if I have a real solutiuon or not, but my next effort is to try switching power supplies. It has an old generic 300W. I think that is probably the final solution. I'll let you know.