It's been a while since I last had to fiddle with this, so I'm working from memory.
So, the WiFi was working before, but stopped when the router was changed.
I think that the answer may lie in "iwconfig key". You're probably using this (or it's alias "iwconfic enc") already to set the WEP key.
If memory serves, try doing a sequence of commands along the lines of:
iwconfig key open
iwconfig key InsertWEPKeyHere
iwconfig essid MYESSID
And this may just work out of the box.
On a distro related note, I've had hold of a couple of Acer laptops recently. I'm typing this in on a Travelmate 382tmi which has a Centrino ipw2200 wifi chip in it. I think the previous Acer was a Travelmate 2304, which had the Broadcom device in it. In both cases I installed Ubuntu (Warty on the 2304, Hoary on the 384), and the WiFi card worked out of the box.
If the earlier tip didn't solve your problem, maybe you could try booting the Ubuntu 5.04 Live CD and see how that configures the WiFi? The King Of HArdware Detecting Live CDs, Knoppix, may be another one that you could try. The idea being that you could see how the wifi gets configured without killing your FC3 installation.
Hope this helps...