Just an update: I fixed the problem. Seems it was a d3d9.dll error. I updated DirectX 9 and everything works great.
That seemed a bit odd, considering I have less (far less) system than you, and don't have that issue (Windows 7 64-bit build 7232).
I have a Celeron DC E1200 (overclocked to 2.67 GHz), 3 GB of RAM, and an HIS HD3450 PCIe card driving an Acer H233H 23" display at the full-tilt 1920x1080 NI (the default for the display, and for GC).
I'm having major issues with the second mission (the Yor) putting me into a weird one-colony-and-broke loop (though I start out with two colonies, the Yor sneak in and capture one, despite the Arnorian Battle Cruiser, which let me beat the Yor down otherwise, and this on Cakewalk, since I'm new to ToA and to Campaign Mode).
Is this a bug unique to Cakewalk? Or is there something I'm doing wrong?