It looks ominous now, but I think it would be a mistake to assume that the Muslim population will not eventually fall to the same pressures that inevitably exert themselves upon populations... forces that eventually slow their growth... hopefully such forces will exert themselves before western culture is completely overrun.
Hopefully, western education and western prosperity will act to dilute of religious militance.... just as it tends to do with other religious traditions. Prosperity/knowledge ultimately lead to rejection of religion (or at least the more militant aspects of it, with a few exceptions), and a greater intellectual humility. The incentives to reproduce will lessen as prosperity increases, and as religious motives behind reproduction decrease. Its really hard to see how Muslims will maintain such large families in western societies indefinitely. Same with Mexicans. Something will give, eventually.
The best thing we could do is make sure Muslims get a good education, and equal opportunity. You guys will be praying for more of those good ol atheist professors at Universities.;)