You certainly aren't the first person who has experienced this.
First, look at the
It appears that when the temperature dips below 30 F the resistive value in passlock system also drops so the car won't start (see the 3/16/07 entry here http://www.carsurvey.org/viewcomments_r
It looks like the only way to bypass the passlock is to install a passlock bypass module. Here's a good resource for the module http://members.tripod.com/~alarmtek/VAT
This has also been discussed in the Saturn Ion Starting Problems discussion listed below.
Source: Saturn Ion Starting Problems http://townhall-talk.edmunds.com/direct