The Samsung Vibrant (the first of the original Galaxy S devices to hit the U.S.) is no longer supported by CyanogenMod. According to developer Abhisek Devkota, issues with the way the radio interface layer interacts with the audio layer leads to a loss of the ability to dial 911, and this issue can not be solved without source code from Samsung. In his own words:
We are no longer supporting the Vibrant due to the inability to dial 911. We consider the issues related to this unresolvable without source code from Samsung related to the Radio interface layer and its interactions with the Audio layers and have taken the decision to no longer support this. We apologize for the inconvenience and strongly suggest that Vibrant users use a Samsung ROM due to the 911 issues with any ROMs based on open source code.
We'll have to second his recommendation -- if you're currently using CM or another AOSP-based ROM on your Vibrant, you should look at Samsung TouchWiz based ROMs as an alternative. Having cool open-source software on your phone is great, but not at the expense of losing the ability to call emergency services. It was fun while it lasted though, and thanks for all the hard work gentlemen!
Source: +Abhisek Devkota