Comment 11 for bug 263255

Dunno if this helps, but I tried again with a fairly up-to-date Intrepid system, and the crash doesn't happen any more (the Routes window is opened as expected, both for the existing eth0 connection and for a new, not yet saved Wifi connection).
So for me, the bug is already fixed even without using the packages from https://edge.launchpad.net/~network-manager/+archive.