Use the modem's address instead. It's probably 192.168.0.1 or 192.168.1.1.
Westell's setup software adds an entry into your Windows HOSTS file so "launchmodem" is equivalent to the modem's address. Perhaps this fact will reveal why it's not working now (ever run Westell setup software on that computer? Ever modify your HOSTS file?)
If you've placed a router between your PCs and the modem it's not easy to get to the modem page at all and virtually impossible if the modem and router are in the same subnet (like 192.168.1.x). I suspect this is your problem.
Hook up directly to the modem or get very creative (I used to bypass a router with a 2nd router to do exactly this).